Implantable medical device with flat aluminum electolytic capacitor

ABSTRACT

An implantable medical device such as a defibrillator is described. The device includes an hermetically sealed housing containing a flat electrolytic capacitor and an energy source such as a battery. The battery is connected to the capacitor and provides charge thereto. The capacitor stores the charge at a relatively high voltage. The charge stored in the capacitor is discharged through a defibrillation lead to a site on or in the heart when fibrillation of the heart is detected by the implantable medical device. Methods of making and using the implantable medical device, the capacitor, and their various components are disclosed.

RELATED APPLICATION

This application claims priority and other benefits from U.S.Provisional Patent Application Serial No. 60/080,564 filed Apr. 3, 1998entitled "Flat Aluminum Electrolytic Capacitor."

FIELD OF THE INVENTION

This invention relates to implantable medical devices such asdefibrillators and AIDs, and their various components, including flatelectrolytic capacitors for same, and corresponding methods of makingand using same.

BACKGROUND OF THE INVENTION

Implantable medical devices for therapeutic stimulation of the heart arewell known in the art. In U.S. Pat. No. 4,253,466 issued to Hartlaub etal., for example, a programmable demand pacemaker is disclosed. Thedemand pacemaker delivers electrical energy, typically ranging inmagnitude between about 5 and about 25 micro Joules, to the heart toinitiate the depolarization of cardiac tissue. This stimulating regimeis used to treat heart block by providing electrical stimulation in theabsence of naturally occurring spontaneous cardiac depolarizations.

Another form of implantable medical device for therapeutic stimulationof the heart is an automatic implantable defibrillator (AID), such asthose described in U.S. Patent No. Re. 27,757 to Mirowski et al. andU.S. Pat. No. 4,030,509 to Heilman et al. Those AID devices deliverenergy (about 40 Joules) to the heart to interrupt ventricularfibrillation of the heart. In operation, an AID device detects theventricular fibrillation and delivers a nonsynchronous high-voltagepulse to the heart through widely spaced electrodes located outside ofthe heart, thus mimicking transthoracic defibrillation. The technique ofHeilman et al. requires both a limited thoracotomy to implant anelectrode near the apex of the heart and a pervenous electrode systemlocated in the superior vena cava of the heart.

Another example of a prior art implantable cardioverter includes thepacemaker/cardioverter/defibrillator (PCD) disclosed in U.S. Pat. No.4,375,817 to Engle et al. This device detects the onset oftachyarrhythmia and includes means to monitor or detect the progressionof the tachyarrhythmia so that progressively greater energy levels maybe applied to the heart to interrupt a ventricular tachycardia orfibrillation.

Another device is an external synchronized cardioverter, such as thatdescribed in "Clinical Application of Cardioversion" in CardiovascularClinics, 1970, Vol. 2, pp. 239-260 by Douglas P. Zipes. This type ofexternal device provides cardioversion shocks synchronized withventricular depolarization to ensure that the cardioverting energy isnot delivered during the vulnerable T-wave portion of the cardiac cycle.

Another example of a prior art implantable cardioverter includes thedevice disclosed in U.S. Pat. No. 4,384,585 to Douglas P. Zipes. Thisdevice includes circuitry to detect the intrinsic depolarizations ofcardiac tissue and pulse generator circuitry to deliver moderate energylevel stimuli (in the range of about 0.1 to about 10 Joules) to theheart synchronously with the detected cardiac activity.

The functional objective of such a stimulating regimen is to depolarizeareas of the myocardium involved in the genesis and maintenance ofre-entrant or automatic tachyarrhythmias at lower energy levels withgreater safety than was possible with nonsynchronous cardioversion.Nonsynchronous cardioversion always incurs the risk of precipitatingventricular fibrillation and sudden death. Synchronous cardioversiondelivers the shock at a time when the bulk of cardiac tissue is alreadydepolarized and is in a refractory state. Other examples of automaticimplantable synchronous cardioverters include those of Charms in U.S.Pat. No. 3,738,370.

It is expected that the increased safety deriving from use of lowerenergy levels and their attendant reduced trauma to the myocardium, aswell as the smaller size of implantable medical devices, will expandindications for use beyond the existing patient base of automaticimplantable defibrillators. Since many episodes of ventricularfibrillation are preceded by ventricular (and in some cases,supraventricular) tachycardias, prompt termination of the tachycardiamay prevent ventricular fibrillation.

Consequently, current devices for the treatment of tachyarrhythmiasinclude the possibility of programming staged therapies ofantitachycardia pacing regimens, along with cardioversion energy anddefibrillation energy shock regimens in order to terminate thearrhythmia with the most energy-efficient and least traumatic therapies,when possible. In addition, some current implantable tachycardia devicesare capable of delivering single or dual chamber bradycardia pacingtherapies, as of which are described, for example, in U.S. Pat. No.4,800,833 to Winstrom, U.S. Pat. No. 4,830,006 to Haluska et al., andU.S. patent application Ser. No. 07/612,758 to Keimel for "Apparatus forDelivering Single and Multiple Cardioversion and Defibrillation Pulses"filed Nov. 14, 1990, and incorporated herein by reference in itsentirety. Furthermore, and as described in the foregoing '833 and '006patents and the '758 application, considerable study has been undertakento devise the most efficient electrode systems and shock therapies.

Initially, implantable cardioverters and defibrillators were envisionedas operating with a single pair of electrodes applied on or in theheart. Examples of such systems are disclosed in the aforementioned '757and '509 patents, wherein shocks are delivered between an electrode isplaced in or on the right ventricle and a second electrode placedoutside the right ventricle. Studies have indicated that two electrodedefibrillation systems often require undesirably high energy levels toeffect defibrillation.

In an effort to reduce the amount of energy required to effectdefibrillation, numerous suggestions have been made with regard tomultiple electrode systems. Some of those suggestions are set forth inU.S. Pat. No. 4,291,699 to Geddes et al., U.S. Pat. No. 4,708,145 toTacker et al., U.S. Pat. No. 4,727,877 to Kallock, and U.S. Pat. No.4,932,407 issued to Williams where sequential pulse multiple electrodesystems are described. Sequential pulse systems operate based on theassumption that sequential defibrillation pulses delivered betweendiffering electrode pairs have an additive effect such that the overallenergy requirements to achieve defibrillation are less than the energylevels required to accomplish defibrillation using a single pair ofelectrodes.

An alternative approach to multiple electrode sequential pulsedefibrillation is disclosed in U.S. Pat. No. 4,641,656 to Smits and alsoin the above-cited '407 patent. This defibrillation method mayconveniently be referred to as a multiple electrode simultaneous pulsedefibrillation method, and involves the simultaneous delivery ofdefibrillation pulses between two different pairs of electrodes. Forexample, one electrode pair may include a right ventricular electrodeand a coronary sinus electrode, and a second electrode pair may includea right ventricular electrode and a subcutaneous patch electrode, withthe right ventricular electrode serving as a common electrode to bothelectrode pairs. An alternative multiple electrode, single path,biphasic pulse system is disclosed in U.S. Pat. No. 4,953,551 to Mehraet al., which employs right ventricular, superior vena cava andsubcutaneous patch electrodes.

In the above-cited prior art simultaneous pulse multiple electrodesystems, delivery of simultaneous defibrillation pulses is accomplishedby simply coupling two electrodes together. For example, in theabove-cited '551 patent, the superior vena cava and subcutaneous patchelectrodes are electrically coupled together and a pulse is deliveredbetween those two electrodes and the right ventricular electrode.Similarly, in the above-cited '407 patent, the subcutaneous patch andcoronary sinus electrodes are electrically coupled together, and a pulseis delivered between these two electrodes and a right ventricularelectrode. See also U.S. Pat. Nos. 5,411,539; 5,620,477; 5,6589,321;5,545,189 and 5,578,062, where active can electrodes are discussed.

The aforementioned '758 application discloses a pulse generator for usein conjunction with an implantable cardioverter/defibrillator which iscapable of providing all three of the defibrillation pulse methodsdescribed above, with a minimum of control and switching circuitry. Theoutput stage is provided with two separate output capacitors which aresequentially discharged during sequential pulse defibrillation andsimultaneously discharged during single or simultaneous pulsedefibrillation. The complexity of those stimulation therapy regimensrequire rapid and efficient charging of high voltage output capacitorsfrom low voltage battery power sources incorporated within theimplantable medical device.

Typically, the electrical energy required to power an implantablecardiac pacemaker is supplied by a low voltage, low current drain,long-lived power source such as a lithium iodine pacemaker battery ofthe type manufactured by Wilson Greatbatch, Ltd. or Medtronic, Inc.While the energy density of such power sources is typically relativelyhigh, they are generally not capable of being rapidly and repeatedlydischarged at high current drains in the manner required to directlycardiovert the heart with cardioversion energies in the range of 0.1 to10 Joules. Moreover, the nominal voltage at which such batteries operateis generally too low for cardioversion applications. Higher energydensity battery systems are known which can be more rapidly or moreoften discharged, such as lithium thionyl chloride power sources.Neither of the foregoing battery types, however, may have the capacityor the voltage required to provide an impulse of the required magnitudeon a repeatable basis to the heart following the onset oftachyarrhythmia.

Generally speaking, it is necessary to employ a DC-DC converter toconvert electrical energy from a low voltage, low current power supplyto a high voltage energy level stored in a high energy storagecapacitor. A typical form of DC-DC converter is commonly referred to asa "flyback" converter which employs a transformer having a primarywinding in series with the primary power supply and a secondary windingin series with the high energy capacitor. An interrupting circuit orswitch is placed in series with the primary coil and battery. Chargingof the high energy capacitor is accomplished by inducing a voltage inthe primary winding of the transformer creating a magnetic field in thesecondary winding. When the current in the primary winding isinterrupted, the collapsing field develops a current in the secondarywinding which is applied to the high energy capacitor to charge it. Therepeated interruption of the supply current charges the high energycapacitor to a desired level over time.

In U.S. Pat. No. 4,548,209 to Wielders et al. and in theabove-referenced '883 patent, charging circuits are disclosed whichemploy flyback oscillator voltage converters which step up the powersource voltage and apply charging current to output capacitors until thecapacitor voltage reaches a programmed shock energy level.

In charging circuit 34 of FIG. 4 in the '209 patent, twoseries-connected lithium thionyl chloride batteries 50 and 52 areconnected to primary coil 54 of transformer 56 and to power FETtransistor switch 60. Secondary coil 58 is connected through diode 62 tocardioversion energy storage capacitor 64. In this circuit, the flybackconverter works generally as follows: When switch 60 is closed, currentI_(p) passing through primary winding 54 increases linearly as afunction of the formula V_(p) =L_(p) dl/dt. When FET 60 is opened, theflux in the core of transformer 56 cannot change instantaneously, and socomplimentary current I_(s) (which is proportional to the number ofwindings in primary and secondary coils 54 and 58, respectively) startsto flow in secondary winding 58 according to the formula I_(s) =(N_(p)/N_(S))I_(p). Simultaneously, voltage in the secondary winding isdeveloped according to the function V_(s) =L_(s) dl_(s) /dt, therebycausing charging of cardioversion energy storage capacitor 64 to aprogrammed voltage.

The Power FET 60 is switched "on" at a constant frequency of 32 KHz fora duration or duty cycle that varies as a function of the voltage of theoutput capacitor reflected back into the primary coil 54 circuit. Theon-time of power FET 60 is governed by the time interval between thesetting and resetting of flip-flop 70, which in turn is governed eitherby current I_(p) flowing through primary winding 54 or as a function ofa time limit circuit containing further circuitry to vary the time limitwith battery impedance (represented schematically by resistor 53). Inboth cases, the on-time varies from a maximum to a minimum interval asthe output circuit voltage increases to its maximum value.

The aforementioned '883 and '006 patents disclose a variable duty cycleflyback oscillator voltage converter, where the current in the primarycoil circuit (in the case of the '883 patent) or the voltage across asecondary coil (in the case of the '006 patent) is monitored to controlthe duty cycle of the oscillator. In the '883 circuit the "on" time ofthe oscillator is constant and the "off" time varies as a function ofthe monitored current through the transformer.

In the '006 patent, a secondary coil is added to power a high voltageregulator circuit that provides V+ to a timer circuit and components ofthe high voltage oscillator. This high voltage power source allows theoscillator circuit to operate independently of the battery sourcevoltage (which may deplete over time). The inclusion of a furthersecondary winding on an already relatively bulky transformer isdisadvantageous from size and efficiency standpoints.

Energy, volume, thickness and mass are critical features in the designof implantable cardiac defibrillators (ICDs). One of the componentsimportant to optimization of those features is the high voltagecapacitors used to store the energy required for defibrillation. Suchcapacitors typically deliver energy in the range of about 25 to 40Joules, while ICDs typically have a volume of about 40 to about 60 cc, athickness of about 13 mm to about 16 mm and a mass of approximately 100grams.

It is desirable to reduce the volume, thickness and mass of suchcapacitors and devices without reducing deliverable energy. Doing so isbeneficial to patient comfort and minimizes complications due to erosionof tissue around the device. Reductions in size of the capacitors mayalso allow for the balanced addition of volume to the battery, therebyincreasing longevity of the device, or balanced addition of newcomponents, thereby adding functionality to the device. It is alsodesirable to provide such devices at low cost while retaining thehighest level of performance.

Most ICDs employ commercial photoflash capacitors similar to thosedescribed by Troup in "Implantable Cardioverters and Defibrillators,"Current Problems in Cardiology, Volume XIV, Number 12, Dec. 1989, YearBook Medical Publishers, Chicago, and U.S. Pat. No. 4,254,775 for"Implantable Defibrillator and Package Therefor". The electrodes in suchcapacitors are typically spirally wound to form a coiled electrodeassembly. Most commercial photoflash capacitors contain a core ofseparator paper intended to prevent brittle anode foils from fracturingduring coiling. The anode, cathode and separator are typically woundaround such a paper core. The core limits both the thinness and volumeof the ICDs in which they are placed. The cylindrical shape ofcommercial photoflash capacitors also limits the volumetric packagingefficiency and thickness of an ICD made using same.

As noted above, electrodes and separators used in the assembly ofphotoflash capacitors are typically coiled, with a resulting cylindricalcapacitor geometry. Anodes employed in photoflash capacitors typicallycomprise one or two layers of a high purity (99.99%), porous, highlyetched, anodized aluminum foil. Cathode layers in such capacitors areformed of a nonporous, highly etched aluminum foil which may be somewhatless pure (99.7%) respecting aluminum content than the anode layers. Thethickness of such foils is on the order of 100 micrometers and 20micrometers for anode foils and cathode foils, respectively. Thecapacitance of the cathode is balanced respecting that of the anode toensure reliable performance over the life of the device. Separating theanode and cathode is a separator material that typically comprises twolayers of Kraft paper.

Prior art electrolytic capacitors generally include a laminatecomprising an etched aluminum foil anode, an aluminum foil of filmcathode and a Kraft paper or fabric gauze spacer impregnated with asolvent based liquid electrolyte interposed therebetween. A layer ofoxide is formed on the aluminum anode, preferably during passage ofelectrical current through the anode. The oxide layer functions as adielectric layer. The entire laminate is rolled up into the form of asubstantially cylindrical body and encased, with the aid of suitableinsulation, in an aluminum tube or can subsequently sealed with a rubbermaterial.

The energy of the capacitor is stored in the electromagnetic fieldgenerated by opposing electrical charges separated by an aluminum oxidelayer disposed on the surface of the anode. The energy so stored isproportional to the surface area of the aluminum anode. Thus, tominimize the overall volume of the capacitor one must maximize anodesurface area per unit volume without increasing the capacitor's overall(i.e., external) dimensions. Separator material, anode and cathodeterminals, internal packaging and alignment features and cathodematerial further increase the thickness and volume of a capacitor.Consequently, those and other components in a capacitor limit the extentto which its physical dimensions may be reduced.

Recently developed flat aluminum electrolytic capacitors have overcomesome disadvantages inherent in commercial cylindrical capacitors. Forexample, U.S. Pat. No. 5,131,388 to Pless et. al. discloses a relativelyvolumetrically efficient flat capacitor having a plurality of planarlayers arranged in a stack. Each layer contains an anode layer, acathode layer and means for separating the anode layers and cathodelayers (such as paper). The anode layers and the cathode layers areelectrically connected in parallel.

In a recent paper "High Energy Density Capacitors for ImplantableDefibrillators" presented at CARTS 96: 16th Capacitor and ResistorTechnology Symposium, Mar. 11-15 1996, several improvements in thedesign of flat aluminum electrolytic capacitors are described. Describedare the use of a solid adhesive electrolyte for strengthening theseparator and allowing use of a thinner separator. Also described are atriple anode formed from a non-porous foil disposed between two porousfoils. By increasing the number of anode foils per anode layer, thetotal number of separator and cathode layers in a given stack assemblyis reduced, thereby decreasing thickness and volume. Next described arean embedded anode layer tab, where a notch is cut in the anode and a tabof the same thickness as the center anode is placed in the notch. Threeanode layers are welded to one another and to the tabs by a cold weldingprocess. See also U.S. Pat. Nos. 5,562,801; 5,153,820; 5,146,391;5,086,374; 4,942,501; 5,628,801 and 5,584,890 to MacFarlane et al.

In U.S. Pat. No. 5,522,851 to Fayram, manufacturing improvements in flatcapacitors relating to the use of internal alignment elements aredisclosed. Internal alignment elements are employed as a means forcontrolling the relative edge spacing of electrode layers and thehousing. In the absence of such alignment elements, precision assemblyby hand may be required, thereby increasing manufacturing costs. Thehousing size must also be increased to provide tolerance for alignmenterrors, resulting in a bulkier device. The '851 patent also describesthe use of an electrically conductive housing for grounding somecapacitor elements, such as the cathode terminal.

A segment of today's ICD market employs flat capacitors to overcome someof the packaging and volume disadvantages associated with cylindricalphotoflash capacitors. Examples of such flat capacitors are described inthe '388 patent to Pless et al. for "Implantable Cardiac Defibrillatorwith Improved Capacitors," and the '851 patent to Fayram for "Capacitorfor an Implantable Cardiac Defibrillators" Additionally, flat capacitorsare described in a paper entitled "High Energy Density Capacitors forImplantable Defibrillators" by P. Lunsmann and D. MacFarlane presentedat the 16th Capacitor and Resistor Technology Symposium.

Anodes and cathodes of aluminum electrolytic capacitors generally havetabs extending beyond their perimeters to facilitate electricalconnection in parallel. In U.S. Pat. No 4,663,824 to Kenmochi, tabterminal connections for a wound capacitor are described as being laserwelded to feedthrough terminals. Wound capacitors usually contain two orno tabs joined together by crimping or riveting. Termination of largernumbers of anode tabs is described in the '851 patent as beingaccomplished through laser welding of the free ends of the tabs,followed by welding of the tabs to an inner terminal. In the '851patent, cathode tabs are connected by ultrasonic welding to a step inthe capacitor housing.

In assembling a capacitor, it is necessary that the anode and cathoderemain separated electrically to prevent short circuiting. It is alsoimportant that a minimum separation between the anode and cathode bemaintained to prevent arcing between the anode and cathode, or betweenthe anode and the case. In cylindrical capacitors, such spacing istypically maintained at the electrode edges or peripheries by providingseparator overhang at the top and bottom of the anode and cathodewinding. In addition, the anode and cathode are aligned precisely andcoiled tightly to prevent movement of the anode, cathode and separatorduring subsequent processing and use. In flat capacitors, anode tocathode alignment is typically maintained through the use of internalalignment posts (as described, for example, in the '851 patent to Plesset al.) screws (see the '851 patent to Pless et al.) or by using anadhesive electrolyte (see the patents to MacFarlane, supra).

Sealing of capacitor housings is typically accomplished in a variety ofways. Aultman et al. in U.S. Pat. No. 4,521,830 describes a typicalaluminum electrolytic capacitor construction employed from about 1960 toabout 1985. Those typical constructions employed a plastic header withtwo molded-in threaded aluminum terminals of the type shown in Collinset al. in U.S. Pat. No. 3,789,502, where plastic is molded around theterminals. Zeppieri in U.S. Pat. No. 3,398,333 and Schroeder in U.S.Pat. No. 4,183,600 teach prior art capacitors in which an aluminumserrated shank terminal extends through a thermal plastic header. Inboth patents the aluminum terminal is resistance-heated to a temperaturesuch that the length of the terminal is collapsed and the centerdiameter is increased to press the serrations into the melted plastic.Aultman teaches a header design employing a compression-fit set ofterminals disposed in a polymer header.

Hutchins et al. in U.S. Pat No. 4,987,519 describe a glass-to-metal sealterminal connection with a tantalum outer ring being laser welded intoan aluminum case. Kenmochi in U.S. Pat. No. 4,663,824 describes the useof a resin casing that has been previously formed from epoxy, siliconresin, polyoxybenzylene, polyether etherkeytone, or polyether sulfone,and that has high heat resistance. The terminals perforate the walls bymolding them into the casing.

Pless et al. in U.S. Pat. No. 5,131,388 describe the use of a polymerenvelope for encasement of the stack and feedthroughs. A siliconadhesive is used to seal the envelope at the seams. Thepolymer-enveloped flat stack is then disposed within a stainless steelor Titanium case. Aluminum capacitor terminals are described as beingcrimped or welded to the feedthroughs. Fayram in U.S. Pat. No. 5,522,851does not specifically address the issue of feedthrough design. An anodepost is described as being electrically insulated from the housing.

U.S. Pat. No. 4,041,956 to Purdy et al. for "Pacemakers of Low Weightand Method of Making Such Pacemakers"; U.S. Pat. No. 4,692,147 to Dugganfor "Drug Administration Device"; and U.S. Pat. No. 5,456,698 to Bylandet al. for "Pacemaker" disclose various means of hermetically sealinghousings for implantable medical devices, including laser welding means.

Various types of flat and spirally-wound capacitors are known in theart, some examples of which may be found in the issued U.S. Patentslisted in Table 1 below.

                  TABLE 1                                                         ______________________________________                                        Prior Art Patents                                                             U.S. Pat. No.                                                                          Title                                                                ______________________________________                                        3,398,333                                                                              Electrical Component End Seal                                        3,789,502                                                                                    Fused Cathode Electrolytic Capacitors and Method of                                    Making the Same                                       4,183,600                                                                                    Electrolytic Capacitor Cover-Terminal Assembly                 4,385,342                                                                                    Flat Electrolytic Capacitor                                    4,521,830                                                                                    Low Leakage Capacitor Header and Manufacturing                                         Method Therefor                                       4,546,415                                                                                    Heat Dissipation Aluminum Electrolytic Capacitor               4,663,824                                                                                    Aluminum Electrolytic Capacitor and a Manufacturing                                    Method Therefor                                       4,942,501                                                                                    Solid Electrolyte Capacitors and Methods of Making the                                 Same                                                  4,987,519                                                                                    Hermetically Sealed Aluminum Electrolytic Capacitor            5,086,374                                                                                    Aprotic Electrolyte Capacitors and Methods of Making                                   the Same                                              5,131,388                                                                                    Implantable Cardiac Defibrillator with Improved                                        Capacitors                                            5,146,391                                                                                    Crosslinked Electrolyte Capacitors and Methods of                                      Making the Same                                       5,153,820                                                                                    Crosslinked Electrolyte Capacitors and Methods of                                      Making the Same                                       5,324,910                                                                                    Welding Method of Aluminum Foil                                5,370,663                                                                                    Implantable Cardio-Stimulator With Flat Capacitor              5,380,341                                                                                  Solid State Electrochemical Capacitors and Their                                       Preparation                                             5,545,184                                                                                  Cardiac Defibrillator with High Energy Storage                                         Antiferroelectric Capacitor                             5,522,851                                                                                  Capacitor for an Implantable Cardiac Defibriliator               5,584,890                                                                                  Methods of Making Multiple Anode Capacitors                      5,628,801                                                                                  Electrolyte Capacitor and Method of Making the Same              5,660,737                                                                                  Process for Making a Capacitor FoiI with Enhanced                                      Surface Area                                            ______________________________________                                    

As those of ordinary skill in the art will appreciate readily uponreading the Summary of the Invention, Detailed Description of thePreferred Embodiments and Claims set forth below, at least some of thedevices and methods disclosed in the patents of Table 1 and elsewhereherein may be modified advantageously in accordance with the teachingsof the present invention.

SUMMARY OF THE INVENTION

The present invention has certain objects. That is, the presentinvention provides solutions to many problems existing in the prior artrespecting flat electrolytic capacitors for implantable medical devices.Those problems generally include one or more of the following: (a)out-gassing or fluid leakage from capacitor cases, resulting in damageto electronic circuitry contained within implantable medical devices;(b) poor or insufficient recharging times in discharged capacitors; (c)insufficient or marginal overall capacitor capacities; (d) decreasingvoltage or capacity of capacitors with age; (e) volumetricallyinefficient electrode packaging in capacitors; (f) heavy capacitorweights; (g) large physical sizes and volumes of capacitors; (h)expensive manufacturing processes; (i) difficulty in registeringcapacitor electrode assembly elements, and (j) expensive and unreliablecapacitor sealing methods and structures.

Some embodiments of the invention have certain features generally,including at least one of: (a) an implantable cardiac defibrillatorcomprising an energy source, a flat electrolytic capacitor and meanscoupled to the energy source for charging the capacitor; (b) a capacitorcomprising a planar layered structure of anode layers, cathode layersand separator layers separating the anode layers from the cathodelayers; (c) a plurality of anode sub-assemblies electrically connectedin parallel, and a plurality of cathode layers electrically connected inparallel.; (d) a plurality of anode sub-assemblies and the plurality ofcathode layers that are interleaved, separated by interposed separatorlayers and impregnated or covered with a solid or liquid electrolyte toform an electrode assembly; (e) an anode sub-assembly comprising atleast two anode layers; (f) at least one anode layer in an anodesub-assembly having a registration tab extending from a perimeterthereof; (g) at least one cathode layer having a registration tabextending from a perimeter thereof; (h) registration tabs for connectinganode sub-assemblies or cathode layers in parallel electrically; (i)registration tabs for connecting anode sub-assemblies or cathode layersto feedthroughs; (j) anode and cathode layers comprising aluminum foil;(k) separator layers comprising paper; (k) an aluminum case having anopen end for receiving an electrode assembly therewithin; and (l) a casecrimpingly or weldingly sealed with a cover.

Particular aspects of the various methods and apparatus of the presentinvention have at least some of the objects, features and advantagesdescribed below.

A first apparatus and corresponding methods of the present inventionprovide at least some solutions to problems existing in prior artcapacitors for AIDs, including prior art capacitors that: (a) are proneto electrical shorting between adjacent anode and cathode layers due tothe presence of burrs along the edges of cut electrode layers; (b) areprone to electrical shorting between adjacent anode and cathode layersdue to the generation of metal particulates during electrode layercutting processes; and (c) are costly to manufacture due to the largenumber of components they contain and the relatively slow manufacturingtechniques employed to construct them.

Some embodiments of the first apparatus and corresponding methods of thepresent invention have certain features, including at least one of: (a)very low clearance dies for cutting capacitor electrode foil materialsto form electrode layers; (b) die punches having faces not parallel tothe corresponding floor of a cutting die for cutting capacitor electrodefoil materials to form electrode layers; (c) upward die punch motions tocut capacitor foil materials to form electrode layers; and (d) use ofair, gas or vacuum systems to clear debris from cut electrode layers.

In respect of known flat electrolytic capacitors, the first apparatusand corresponding methods of the present invention provide advantages,including one or more of: (a) formed electrode layers having a minimumnumber and size of edge burrs; (b) electrode foil material cutting andelectrode layer forming methods well suited for high speed manufacturingmethods; (c) electrode foil material cutting and electrode layer formingmethods resulting in reduced cutting debris; and (d) electrode foilmaterial and electrode layer forming methods producing reduced amountsof cutting debris on the surfaces of the electrode layers.

A second apparatus and corresponding methods of the present inventionprovide at least some solutions to problems existing in prior artcapacitors for AIDs, including capacitors that: (a) add extra, inertvolume in the form of alignment elements disposed within the capacitorcase for registering electrode layers and assemblies; (b) provide meansfor aligning electrode layers that are too imprecise to permit theamount of paper overhang in electrode layers to be reduced; (c) may notbe manufactured using high speed manufacturing techniques; (d) includemany piece parts and therefore increase manufacturing costs.

Some embodiments of the second apparatus and corresponding methods ofthe present invention have certain features, including at least one of:(a) tooling and corresponding methods for capturing and aligningelectrode tabs and aligning electrode layers; (b) robotic assemblymethods for constructing electrode assemblies; (c) a capacitor designthat does not require the use of inactive or inert alignment elementsdisposed within the capacitor case.

In respect of known flat electrolytic capacitors, the second apparatusand corresponding methods of the present invention provide advantages,including one or more of: (a) a more volumetrically efficient mechanicaldesign providing lower volume and higher energy density; (b) amechanical design and method for constructing electrode assemblies thatpermits the use of high speed manufacturing techniques; (c) lower costcapacitors owing to increased manufacturing efficiencies; (d) simpleelectrode layer and assembly plate geometries, resulting in fewer pieceparts and lower cost; and (e) a case having fewer points from whichelectrolyte may leak.

A third apparatus and corresponding methods of the present inventionprovide at least some solutions to problems existing in prior artcapacitors for AIDs, including capacitors that: (a) have electrodeassemblies having electrode and separator layers that must bemechanically secured together by relatively large volume, inertmechanical means; (b) have electrode assemblies prone to movement withinthe case of the capacitor; (c) have feedthrough connections that may beaffected by movement of the electrode assembly within the case.

Some embodiments of the third apparatus and corresponding methods of thepresent invention have certain features, including at least one of: (a)an electrode assembly secured together by a low-volume electrodeassembly wrap and corresponding adhesive strip; (b) an electrodeassembly secured together by low-volume electrode assembly clamps, bandsor wraps disposed about the periphery of the assembly; (c) an electrodeassembly which expands and is secured against the interior portions of acapacitor can by electrolyte-swelled separator layers; and (d) separatorlayers which envelop or are disposed between electrode layers, theseparator layers having perimeters and surface areas which exceed thoseof the electrode layers.

In respect of known flat electrolytic capacitors, the third apparatusand corresponding methods of the present invention provide advantages,including one or more of: (a) a capacitor having higher energy densityowing to more electrode material of greater surface area being disposedtherewithin; (b) electrode layers having no holes for registrationdisposed therethrough, and therefore having increased surface area; (c)a capacitor not having elaborate, volume-consuming mechanisms forretaining or securing the electrode assembly disposed therewithin, and(d) highly reliable feedthrough connections owing to the electrodeassembly being tightly secured and retained within the case of thecapacitor.

A fourth apparatus and corresponding methods of the present inventionprovide at least some solutions to problems existing in prior artcapacitors for AIDs, including capacitors that: (a) contain anode orcathode tab terminal connections that are difficult to laser weld orotherwise connect or connect to; (b) have tab terminals prone tofracturing during manufacturing; (c) require a two step, and thereforemore costly, method for connecting electrode tabs and for connectingfeedthroughs thereto; and (d) require an excessive number of componentsfor connecting electrode tab bundles to feedthroughs, thereby increasingcost and volume and decreasing volumetric efficiency.

Some embodiments of the fourth apparatus and corresponding methods ofthe present invention have certain features, including at least one of:(a) direct consolidation and connection of multiple electrode layer tabsto a single feedthrough or feedthrough attachment means; (b) directconsolidation and connection of multiple electrode layer tabs to acoiled distal end of a single feedthrough or feedthrough attachmentmeans; (c) welded feedthrough and electrode tab connections using, forexample, laser spot welds, seam welds, ultrasonic welds or resistancewelds; (d) an intermediate component disposed between electrode tabs anda feedthrough for providing strain relief.

In respect of known flat electrolytic capacitors, the fourth apparatusand corresponding methods of the present invention provide advantages,including one or more of: (a) a one-step method for connecting electrodetabs and feedthroughs; (b) a minimum number of components for connectingelectrode tabs to feedthroughs; (c) highly reliable feedthroughconnections; and (d) lower component and manufacturing costs.

A fifth apparatus and corresponding methods of the present inventionprovide at least some solutions to problems existing in prior artcapacitors for AIDs, including capacitors that: (a) are susceptible todamage of internal capacitor components resulting from laser beamsentering the interior of the capacitor case when welding the cover tothe case of the capacitor; (b) require means incorporated into thecapacitor for aligning the cover to the case during sealing operationsthat add inert, unusable volume to the capacitor; (c) require separatemeans for clamping the case and cover together during welding of thecase and cover, thereby increasing manufacturing cycle time and cost;(d) have aluminum cases and covers that are difficult to laser weldtogether in a cost-effective manner yet still produce an hermetic seal;and (e) do not incorporate into the capacitor means for performingleaktightness testing.

Some embodiments of the fifth apparatus and corresponding methods of thepresent invention have certain features, including at least one of: (a)self-alignment and self-engagement elements or structures disposed alongthe joint between the case and the cover and incorporated into thecapacitor to facilitate holding the case and cover together duringwelding and sealing; (b) case and corresponding cover weld joint andcrimp configurations that eliminate or reduce laser beam damage toelectrode assemblies during welding; (c) an optimized set of weldingparameters for joining and sealing the case and cover of a capacitor;(d) an electrolyte fill port that permits standard helium leaktightnesstesting of the integrity of the capacitor seal.

In respect of known flat electrolytic capacitors, the fifth apparatusand corresponding methods of the present invention provide advantages,including one or more of: (a) not being damaged internally by laserbeams employed to weld the case to the cover; (b) having means foraligning and maintaining the positions of the case and cover duringwelding and sealing that add no volume to the capacitor and that requireno additional steps during the welding process; (c) providing arelatively wide window of cost-effective laser welding parameters forhermetically welding the case to the cover; (d) a flat capacitor thatmay be checked for leaktightness using cost-effective standard heliumleak rate test methods.

A sixth apparatus and corresponding methods of the present inventionprovide at least some solutions to problems existing in prior artcapacitors for AIDs, including capacitors that: (a) have no means formaking simple crimped connections to the device; (b) have no hermeticseals for feedthroughs; (c) have external terminal or feedthroughinterconnections that are susceptible to breaking or fracturing when thecapacitor is dropped or vibrated excessively during handling orshipping; (d) have no or limited means for providing cost-effectiveelectrically isolated feedthroughs; (e) have no cost-effective means forconnecting external devices or circuits to the terminals of thecapacitor; (f) have no flexible strain-relieving means for connectingelectrodes to feedthroughs, or feedthroughs to external devices orcircuits; (g) are prone to loss of electrolyte; and (h) susceptible todegradation of electrical properties over time.

Some embodiments of the sixth apparatus and corresponding methods of thepresent invention have certain features, including at least one of: (a)a wire harness assembly having a distal end that permits a wide varietyof connection configurations; (b) crimp or slide contacts for devicelevel connections; (c) a connector module mounted on, attached to orengaging the external surface of a capacitor can or cover; (d) an epoxy-or adhesive-sealed feedthrough; (e) feedthrough ferrules andcorresponding wire guides; (f) a capacitor case, cover, ferrules,feedthroughs and fill port providing a high degree of hermeticity; and(g) means for connecting capacitor feedthroughs to external devices orcircuits that are located away from the case of the capacitor.

In respect of known flat electrolytic capacitors, the sixth apparatusand corresponding methods of the present invention provide advantages,including one or more of: (a) fewer manufacturing steps and relatedlower assembly costs when placing the capacitor within an implantablemedical device; (b) crimp contact or sliding feedthrough contacts thatare easy to connect at the device level; (c) no or little loss ofelectrolyte from the capacitor owing to its high degree of hermeticity;(d) a capacitor having electrical properties which do not degrade overthe lifetime of the implantable medical device within which thecapacitor is disposed; and (e) highly flexible means for accomplishingdevice level interconnection without major redesign of the capacitorterminal structure.

A seventh apparatus and corresponding methods of the present inventionprovide at least some solutions to problems existing in prior artcapacitors for AIDs, including capacitors that: (a) contain means forcold welding electrode layers and tabs to electrode layers that addsignificant thickness to an electrode assembly, thereby increasingoverall thickness of the capacitor and its corresponding implantablemedical device; and (b) means for cold welding electrode layers that arenot adaptable to high speed manufacturing techniques.

Some embodiments of the seventh apparatus and corresponding methods ofthe present invention have certain features, including at least one of:(a) means for restricting out-of-plane material flow in flat electrodelayers during cold welding steps; (b) means for cold welding electrodelayers to one another, and for cold welding separator layers toelectrode layers, that are adaptable to high speed manufacturingmethods; and (c) means for monitoring individual cold weld processingparameters.

In respect of known flat electrolytic capacitors, the seventh apparatusand corresponding methods of the present invention provide advantages,including one or more of: (a) low clearance cold welds in electrode andseparator layers, thereby decreasing the thickness of the capacitor andcorresponding implantable medical device; and (b) adaptability to highspeed manufacturing techniques.

An eighth apparatus and corresponding methods of the present inventionprovide at least some solutions to problems existing in prior artcapacitors for AIDs, including capacitors that: (a) have high equivalentseries resistances; and (b) have relatively low total capacitances.

Some embodiments of the eighth apparatus and corresponding methods ofthe present invention have certain features, including at least one of:(a) a capacitor having relatively low equivalent series resistance; (b)a capacitor having relatively high total capacitance; and (c) acapacitor containing a liquid electrolyte that has undergone successivecycles of being subjected to a vacuum and no vacuum while theelectrolyte is presented to the cell interior to thereby efficiently andrelatively completely saturate the electrode layers of the capacitor.

In respect of known flat electrolytic capacitors, the eighth apparatusand corresponding methods of the present invention provide advantages,including one or more of: (a) a capacitor that is capable of deliveringhigh amounts of charge and energy; (b) a capacitor that rechargesquickly and efficiently; and (c) a capacitor having charge and dischargeperformance that does not appreciably degrade over the lifetime of itscorresponding implantable medical device

Those of ordinary skill in the art will understand immediately uponreferring to the drawings, detailed description of the preferredembodiments and claims hereof that many objects, features and advantagesof the capacitors and methods of the present invention will findapplication in the fields other than the field of implantable medicaldevices.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference is now made to the accompanying detailed drawings of thepreferred embodiments in which like reference numerals represent like orsimilar parts throughout, wherein:

FIG. 1 illustrates the physical components of one embodiment of apacemaker/cardioverter/defibrillator (PCD) and lead system of oneembodiment of the present invention;

FIG. 2 shows a functional block diagram illustrating the interconnectionof voltage conversion circuitry of one embodiment of the presentinvention with primary functional components of one type of animplantable PCD;

FIGS. 3(a)-3(g) are an exploded perspective view of the variouscomponents of one embodiment of the present invention as they aredisposed within the housing of implantable PCD;

FIG. 4 shows an exploded view of one embodiment of a single electrodesub-assembly of a capacitor of the present invention;

FIG. 5(a) shows an exploded perspective view of one embodiment of a coldwelding apparatus in which anode layers of the electrode sub-assembly ofFIG. 4 are cold-welded;

FIG. 5(b) shows an unexploded view of the cold welding apparatus of FIG.5(a);

FIG. 5(c) shows a cross-sectional view of the cold welding apparatus ofFIGS. 5(a) and 5(b) in which anode layers of the electrode sub-assemblyof FIG. 4 are cold-welded therein;

FIG. 6(a) shows an exploded top perspective view of one embodiment of anelectrode assembly of a capacitor of the present invention;

FIG. 6(b) shows a cross-sectional view of a portion of one embodiment ofa cold-welded anode assembly of the present invention;

FIG. 6(c) shows a cross-sectional view of another portion of oneembodiment of a cold-welded anode assembly of the present invention;

FIG. 7 shows a top perspective view of one embodiment of an electrodeassembly of a capacitor of the present invention;

FIG. 8 shows an enlarged view of a portion of the electrode assemblyshown in FIG. 7;

FIG. 9 shows an exploded top perspective view of one embodiment of acapacitor of the present invention employing the electrode assembly ofFIGS. 6, 7 and 8 therein;

FIG. 10 shows an exploded top perspective view of the partiallyassembled capacitor of FIG. 9;

FIG. 11 shows a top view of one embodiment of a fully assembledcapacitor of the present invention having no cover 110 disposed thereon;

FIG. 12 shows a top perspective view of the capacitor of FIG. 11 havingcover 110 disposed thereon.

FIG. 13 shows a flow chart of one method of the present invention formaking a capacitor of the present invention;

FIG. 14 shows a flow chart of one method of the present invention formaking an anode layer of the present invention;

FIG. 15 shows a flow chart of one method of the present invention formaking an electrode assembly of the present invention;

FIG. 16 shows a flow chart of one method of the present invention formaking tab interconnections and feedthrough terminal connections of thepresent invention;

FIG. 17 shows a flow chart of one method of the present invention formaking tab interconnections and feedthrough terminal connections of thepresent invention;

FIG. 18 shows a flow chart of one method of the present invention formaking a case sub-assembly of the present invention;

FIG. 19 shows a flow chart of one method of the present invention forsealing a case and cover of the present invention;

FIG. 20 shows a flow chart of one method of the present invention forsealing a feedthrough of the present invention;

FIGS. 21(a) through 21(e) show perspective, top, cross-sectional, topand cross-sectional views, respectively, of one embodiment of aconnector block of the present invention;

FIG. 22 shows a flow chart of one method of the present invention forvacuum treating an aged capacitor of the present invention;

FIG. 23 shows a flow chart of one method of the present invention forrefilling an aged capacitor of the present invention;

FIG. 24 shows comparative capacitance data for prior art capacitors andcapacitors made according to the methods of FIGS. 22 and 23;

FIG. 25 shows comparative equivalent series resistance (ESR) data forprior art capacitors and capacitors made according to the methods ofFIGS. 22 and 23;

FIGS. 26(a) through 26(p) show various embodiments of the crimp andjoint of the case and cover of the present invention;

FIG. 27(a) shows a top view of a capacitor of the present invention witha portion of its cover removed;

FIG. 27(b) shows an end view of the capacitor of FIG. 27(a), and

FIGS. 28(a) through 28(c) show various views of a liquid electrolytefill port ferrule tube and fill port ferrule of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates one embodiment of implantable PCD 10 of the presentinvention, its associated electrical leads 14, 16 and 18, and theirrelationship to a human heart 12. The leads are coupled to PCD 10 bymeans of multi-port connector block 20, which contains separateconnector ports for each of the three leads illustrated. Lead 14 iscoupled to subcutaneous electrode 30, which is intended to be mountedsubcutaneously in the region of the left chest. Lead 16 is a coronarysinus lead employing an elongated coil electrode which is located in thecoronary sinus and great vein region of the heart. The location of theelectrode is illustrated in broken line format at 32, and extends aroundthe heart from a point within the opening of the coronary sinus to apoint in the vicinity of the left atrial appendage.

Lead 18 is provided with elongated electrode coil 28 which is located inthe right ventricle of the heart. Lead 18 also includes stimulationelectrode 34 which takes the form of an advanceable helical coil whichis screwed into the myocardial tissue of the right ventricle. Lead 18may also include one or more additional electrodes for near and farfield electrogram sensing. A more detailed description of the leadsillustrated can be found in the aforementioned '407 patent. However, theinvention is also believed workable in the context of multiple electrodesystems employing different sets of electrodes, including superior venacava electrodes and epicardial patch electrodes.

In the system illustrated, cardiac pacing pulses are delivered betweenhelical electrode 34 and elongated electrode 28. Electrodes 28 and 34are also employed to sense electrical signals indicative of ventricularcontractions. As illustrated, it is anticipated that the rightventricular electrode 28 will serve as the common electrode duringsequential and simultaneous pulse multiple electrode defibrillationregimens. For example, during a simultaneous pulse defibrillationregimen, pulses would simultaneously be delivered between electrode 28and electrode 30 and between electrode 28 and electrode 32. Duringsequential pulse defibrillation, it is envisioned that pulses would bedelivered sequentially between subcutaneous electrode 30 and electrode28 and between coronary sinus electrode 32 and right ventricularelectrode 28. Single pulse, two electrode defibrillation pulse regimensmay be also provided, typically between electrode 28 and coronary sinuselectrode 32. Alternatively, single pulses may be delivered betweenelectrodes 28 and 30. The particular interconnection of the electrodesto an implantable PCD will depend somewhat on which specific singleelectrode pair defibrillation pulse regimen is believed more likely tobe employed.

FIG. 2 is a block diagram illustrating the interconnection of highvoltage output circuit 40, high voltage charging circuit 64 andcapacitors 265 according to one embodiment of the present invention witha prior art implantable PCD. As illustrated, the device is controlled bymeans of a stored program in microprocessor 42, which performs allnecessary computational functions within the device. Microprocessor 42is linked to control circuitry 44 by means of bidirectional data/controlbus 46, and thereby controls operation of the output circuitry 40 andthe high voltage charging circuitry 64. On reprogramming of the deviceor on the occurrence of signals indicative of delivery of cardiac pacingpulses or of the occurrence of cardiac contractions, pace/sensecircuitry 78 will awaken microprocessor 42 to perform any necessarymathematical calculations, to perform tachycardia and fibrillationdetection procedures and to update the time intervals controlled by thetimers in pace/sense circuitry 78.

The basic operation of such a system in the context of an implantablePCD may correspond to any of the systems known in the art. Moreparticularly, the flat aluminum electrolytic capacitor of the presentinvention may be employed generally in conjunction with the varioussystems illustrated in the aforementioned '209, '585, '006, '883 and'817 patents, or in conjunction with the various systems or componentsdisclosed in U.S. Pat. No. 4,693,253 to Adams, U.S. Pat. No. 5,188,105to Keimel, U.S. Pat. No. 5,591,212 to Keimel, U.S. Pat. No. 5,383,909 toKeimel, U.S. Pat. No. 5,354,316 to Keimel, U.S. Pat. No. 5,336,253 toGordon et al., U.S. Pat. No. 4,384,585 to Zipes, U.S. Pat. No. 4,949,719to Pless et al., U.S. Pat. No. 4,374,817 to Engle et al., U.S. Pat. No.4,577,633 to Berkowitz, U.S. Pat. No. 4,880,005 to Pless et al., U.S.Pat. No. 4,726,380 to Vollmann et al., U.S. Pat. No. 4,587,970 to Holleyet al., U.S. Pat. No. 5,447,519 to Peterson, U.S. Pat. No. 4,476,868 toThompson, U.S. Pat. No. 4,556,063 to Thompson, U.S. Pat. No. 4,379,459to Stein, U.S. Pat. No. 5,312,453 to Wyborny, U.S. Pat. No. 5,545,186 toOlson, U.S. Pat. No. 5,345,316 to Keimel, U.S. Pat. No. 5,314,430 toBardy, U.S. Pat. No. 5,131,388 to Pless, U.S. Pat. No. 3,888,260 toFischell, U.S. Pat. No. 5,411,537 to Munshi et al. and U.S. Pat. No.4,821,723 to Baker et al. All the foregoing patents are herebyincorporated herein by reference in their respective entireties.

Control circuitry 44 provides three signals of primary importance tooutput circuitry 40 of the present invention. Those signals include thefirst and second control signals discussed above, labeled here as ENAB,line 48, and ENBA, line 50. Also of importance is DUMP line 52 whichinitiates discharge of the output capacitors and VCAP line 54 whichprovides a signal indicative of the voltage stored on the outputcapacitors C1, C2, to control circuitry 44. Defibrillation electrodes28, 30 and 32 illustrated in FIG. 1, above, are shown coupled to outputcircuitry 40 by means of conductors 22, 24 and 26. For ease ofunderstanding, those conductors are also labeled as "COMMON", "HVA" and"HVB". However, other configurations are also possible. For example,subcutaneous electrode 30 may be coupled to HVB conductor 26, to allowfor a single pulse regimen to be delivered between electrodes 28 and 30.During a logic signal on ENAB, line 48, a cardioversion/defibrillationpulse is delivered between electrode 30 and electrode 28. During a logicsignal on ENBA, line 50, a cardioversion/defibrillation pulse isdelivered between electrode 32 and electrode 28.

The output circuitry of the present invention includes a capacitor bank,including capacitors C1 and C2 and diodes 121 and 123, used fordelivering defibrillation pulses to the electrodes. Alternatively, thecapacitor bank may include a further set of capacitors as depicted inthe above referenced '758 application. In FIG. 2, capacitors 265 areillustrated in conjunction with high voltage charging circuitry 64,controlled by the control/timing circuitry 44 by means of CHDR line 66.As illustrated, capacitors 265 are charged by means of a high frequency,high voltage transformer 110. Proper charging polarities are maintainedby means of the diodes 121 and 123. VCAP line 54 provides a signalindicative of the voltage on the capacitor bank, and allows for controlof the high voltage charging circuitry and for termination of thecharging function when the measured voltage equals the programmedcharging level.

Pace/sense circuitry 78 includes an R-wave amplifier according to theprior art, or more advantageously as disclosed in co-pending, commonlyassigned U.S. patent application Ser. No. 07/612,670 to Keimel et al.for "Apparatus for Monitoring Electrical Physiological Signals," filedNov. 14, 1990, which is hereby incorporated herein by reference in itsentirety. The present invention is believed workable, however, in thecontext of any known R-wave amplification system. Pace/sense circuitry78 also includes a pulse generator for generating cardiac pacing pulses,which may also correspond to any known cardiac pacemaker outputcircuitry and includes timing circuitry for defining ventricular pacingintervals, refractory intervals and blanking intervals, under control ofmicroprocessor 42 via control/data bus 80.

Control signals triggering generation of cardiac pacing pulses bypace/sense circuitry 78 and signals indicative of the occurrence ofR-waves, from pace/sense circuitry 78 are communicated to controlcircuitry 44 by means of a bi-directional data bus 81. Pace/sensecircuitry 78 is coupled to helical electrode 34 illustrated in FIG. 1 bymeans of a conductor 36. Pace/sense circuitry 78 is also coupled toventricular electrode 28, illustrated in FIG. 1, by means of a conductor82, allowing for bipolar sensing of R-waves between electrodes 34 and 28and for delivery of bipolar pacing pulses between electrodes 34 and 28,as discussed above.

FIGS. 3(a) through 3(g) show perspective views of various components ofimplantable PCD 10 of the present invention, including one embodiment ofthe capacitor of the present invention, as those components are placedsuccessively within the housing of PCD 10. In FIG. 3(a), electronicsmodule 360 is placed in right-hand shield 340 of PCD 10. FIG. 3(b) showsPCD 10 once electronics module 360 has been seated in right-hand shield340.

FIG. 3(c) shows a pair of capacitors 265 of the present invention priorto being placed within right-hand shield 340, the capacitors beingconnected electrically in series by interconnections in electronicsmodule 340. FIG. 3(d) shows PCD 10 once the pair of capacitors 265 hasbeen placed within right-hand shield 340.

FIG. 3(e) shows insulator cup 370 prior to its placement atop capacitors265 in right-hand shield 340. FIG. 3(f) shows electrochemical cell orbattery 380 having insulator 382 disposed therearound prior to battery380's placement in shield 340. Battery 380 provides the electricalenergy required to charge and re-charge capacitors 265, and also powerselectronics module 360.

Battery 380 is most preferably a high-capacity, high-rate,spirally-wound battery of the type disclosed in U.S. Pat. No. 5,439,760to Howard et al. for "High Reliability Electrochemical Cell andElectrode Assembly Therefor" and U.S. Pat. No. 5,434,017 to Berkowitz etal. for "High Reliability Electrochemical Cell and Electrode AssemblyTherefor," the disclosures of which are hereby incorporated by referenceherein in their respective entireties.

Battery 380 may less preferably be a battery having spirally-wound,stacked plate or serpentine electrodes of the types disclosed, forexample, in U.S. Pat. Nos. 5,312,458 and 5,250,373 to Muffoletto et al.for "Internal Electrode and Assembly Method for Electrochemical Cells;"U.S. Pat. No. 5,549,717 to Takeuchi et al. for "Method of makingPrismatic Cell;" U.S. Pat. No. 4,964,877 to Kiester et al. for"Non-Aqueous Lithium Battery;" U.S. Pat. No. 5,147,737 to Post et al.for "Electrochemical Cell with Improved Efficiency Serpentine Electrode"and U.S. Pat. No. 5,468,569 to Pyszczek et al. for "Use of StandardUniform Electrode Components in Cells of Either High or Low Surface AreaDesign," the disclosures of which are hereby incorporated by referenceherein in their respective entireties.

High-rate hybrid cathode cells are particularly suitable for use inconjunction with the capacitor of the present invention. Examples ofhybrid cathode batteries and cells having cathodes comprising lithiumanodes and cathodes containing mixtures of various types of silvervanadium oxide and (CF_(x))_(n), are disclosed in U.S. Pat. No.5,114,810 to Frysz et al.; U.S. Pat. No. 5,180,642 to Weiss et al.; U.S.Pat. No. 5,624,767 to Muffoletto et al.; U.S. Pat. No. 5,639,577 toTakeuchi et al., and U.S. Pat. No. 5,667,916 to Ebel et al., all ofwhich patents are hereby incorporated by reference herein in theirrespective entireties.

In preferred embodiments of batteries suitable for use in conjunctionwith the capacitor of the present invention, it has been discovered thatthe electrolyte most preferably comprises about 1.0 M LiBF₄, the anodemost preferably comprises lithium metal, the cathode most preferablycomprises about 90% by weight active materials (i.e., 90% by weight of amixture of (CF_(x))_(n) and SVO), about 7% by weight polymer binder andabout 3% conductive carbon.

The SVO employed in cells and batteries employed to charge and rechargethe capacitor of the present invention is most preferably of the typeknown as "combination silver vanadium oxide" or "CSVO" as disclosed inU.S. Pat. Nos. 5,221,453; 5,439,760 and 5,306,581 and U.S. patentapplication Ser. No. 08/792,413 filed Feb. 3, 1997 to Crespi et al.,hereby incorporated by reference herein, each in its respectiveentirety.

It is to be understood, however, that any type of suitable silvervanadium oxide (or SVO) may be employed in cathodes and cells used tocharge and recharge capacitors of the present invention, including, butnot limited to, substitute SVO as disclosed by Takeuchi et al. in U.S.Pat. No. 5,472,810 and as disclosed by Leising et al. in U.S. Pat. No.5,695,892, SVO made by the decomposition method as disclosed by Liang etal. in U.S. Pat. Nos. 4,310,609 and 4,391,729, amorphous SVO asdisclosed by Takeuchi et al. in U.S. Pat. No. 5,498,494, SVO prepared bythe sol-gel method as disclosed by Takeuchi et al. in U.S. Pat. No.5,558,680, and SVO prepared by the hydrothermal process.

Additionally, it is preferred that batteries used in conjunction withthe capacitor of the present invention be cathode limited to permitaccurate, reliable prediction of battery end-of-life on the basis ofobserving voltage discharge curves since the discharge characteristicsof cathode-limited cells are relatively uniform.

In its more general aspects, the capacitor of the present invention maybe employed in conjunction with electrochemical cells in which the anodecomprises any active metal above hydrogen in the EMF series, such as analkali or alkaline earth metal or aluminum. Lithium is a preferred anodematerial.

Cathode materials in electrochemical cells suitable for use inconjunction with the capacitor of the present invention are mostpreferably solid and comprise as active components thereof metal oxidessuch as vanadium oxide (V₆ O₁₃), silver vanadium oxide (Ag₂ V₄ O₁₁), ormanganese dioxide. Of those cathode materials, thermally treatedelectrolytic manganese dioxide is most preferred. As mentioned above,the cathode of the electrochemical cell may also comprise carbonmonofluoride (CFx) and hybrids thereof, e.g., CF_(x) +MnO₂, or any otherknown active electrolytic components in combination. By "solid"cathodes, we mean pressed porous solid cathodes, as known in the art.Such cathodes are typically made by mixing one or more active componentswith carbon and poly (tetrafluorethylene) and pressing those componentsto form a porous solid structure.

It is to be understood, however, that battery chemical systems otherthan those set forth explicitly above may be employed in conjunctionwith the capacitor of the present invention, including, but not limitedto, cathode/anode systems such as: silver oxide/lithium; MnO₂ /lithium;V₂ O₅ /lithium; copper silver vanadium oxide/lithium; copperoxide/lithium; lead oxide/lithium; CF_(x) /lithium; chromiumoxide/lithium; bismuth-containing oxides/lithium and lithium ionrechargeable batteries.

FIG. 3(h) shows PCD 10 having left-hand shield 350 connected toright-hand shield 340 and feedthrough 390 projecting upwardly from bothshield halves. Activity sensor 400 and patient alert apparatus 410 areshown disposed on the side lower portion of left-hand shield 350.Left-hand shield 350 and right-hand shield 340 are subsequently closedand hermetically sealed (not shown in the Figures).

FIG. 4 shows an exploded view of one embodiment of a singleanode/cathode sub-assembly 227 capacitor 265 of the present invention.The capacitor design described herein employs a stacked configuration,where anode/cathode sub-assembly 227 comprises alternating substantiallyrectangularly-shaped anode layers 185 and cathode layers 175, withsubstantially rectangularly-shaped separator layers 180 being interposedtherebetween. In one preferred embodiment of the present invention, twoindividual separator layers 180 are disposed between anode sub-assembly170 and cathode layer 175. One anode layer 185a has anode tab 195dattached thereto, more about which we say below. Cathode layer 175d mostpreferably has cathode tab 176 formed integral thereto and projectingfrom the periphery thereof.

The shapes of anode layers 185, cathode layers 175 and separator layers180 are primarily a matter of design choice, and are dictated largely bythe shape or configuration of case 90 within which those layers areultimately disposed. In a die apparatus according to one preferredmethod of the present invention, the punch and cavity of the presentinvention employed in forming those layers should be configured toproduce layers having a desired predetermined shape, such as those shownin FIG. 4. A principal advantage of the capacitor construction of thepresent invention is that anode layers 185, cathode layers 175 andseparator layers 180 may assume any arbitrary shape to optimizepackaging efficiency.

Anode layers 185, cathode layers 175 and separator layers 180 are mostpreferably formed of materials typically used in high quality aluminumelectrolytic capacitors. Individual anode layers 185 are typicallysomewhat stiff and formed of high-purity aluminum processed by etchingto achieve high capacitance per unit area. Cathode layers 175 arepreferably high purity and are comparatively flexible. Paper separators180 are most preferably made slightly larger than cathode layers 175 andanode layers 185 to ensure that a physical barrier is disposed betweenthe anodes and the cathodes of the finished capacitor.

In one embodiment of capacitor 265 of the present invention, and asshown in FIGS. 6 and 9, sub-assembly 227d shown in FIG. 4 is but one ofa plurality of anode/cathode sub-assemblies 227a through 227h disposedwithin capacitor 265. Likewise, a plurality of anode layers 185 andseparator layers 180 is most preferably disposed within eachsub-assembly, while a single cathode layer 175 is disposed within eachsub-assembly 227. FIG. 4 shows anode sub-assembly 170d, one of aplurality of anode sub-assemblies disposed in capacitor 265. Anodesub-assembly 170d in FIG. 4 is but one embodiment of anode sub-assembly170 of the present invention, and is shown therein as most preferablycomprising three unnotched anode layers 185, one notched anode layer 190and one anode tab 195.

It will be understood by those skilled in the art, however, that theprecise number of sub-assemblies 227 selected for use in a givenembodiment of the present invention will depend upon the energy density,volume, voltage, current, energy output and other requirements placedupon capacitor 265. As few as two anode/cathode sub-assemblies 227 andas many as 50 anode/cathode sub-assemblies 227 are included within thescope of the present invention.

Similarly, it will be understood by those skilled in the art that theprecise number of notched and unnotched anode layers 185, anode tabs195, anode sub-assemblies 170, cathode layers 175 and separator layers180 selected for use in a given embodiment of anode/cathode sub-assembly227 of the present invention will depend upon the energy density,volume, voltage, current, energy output and other requirements placedupon capacitor 265.

It will now become apparent that a virtually unlimited number ofcombinations and permutations respecting the number of anode/cathodesub-assemblies 227, and the number of unnotched and notched anode layers185 forming anode sub-assembly 170, anode sub-assemblies 170, anode tabs195, cathode layers 175 and separator layers 180 disposed within eachanode/cathode sub-assembly 227, may be selected according to theparticular requirements of capacitor 265, and further that suchcombinations and permutations fall within the scope of the presentinvention.

Referring to FIG. 4 again, anode sub-assembly 170 most preferablycomprises a plurality of non-notched anode layers 185, notched anodelayer 190, anode tab 195 and anode tab notch 200. Anode layers 185 and190 are formed of anode foil 65 (not shown in the Figures). It has beendiscovered that the anode foil of the present invention is mostpreferably through-etched, has a high specific capacitance (at leastabout 0.3, at least about 0.5 or most preferably at least about 0.8microfarads/cm²), has a dielectric withstand parameter of at least 425Volts DC, a thickness ranging between about 50 and about 200micrometers, more preferably between about 75 and 150 micrometers, morepreferably yet between about 90 and about 125 micrometers, and mostpreferably being about 100 micrometers thick, and a cleanliness of about1.0 mg/m² respecting projected area maximum chloride contamination.

Thin anode foils are preferred in the present invention, especially ifthey substantially maintain or increase specific capacitance whilereducing the thickness of electrode assembly 225, or maintain thethickness of electrode assembly 225 while increasing overallcapacitance. For example, it is contemplated in the present inventionthat individual anode layers 185 have a thickness of about 10micrometers, about 20 micrometers, about 30 micrometers, about 40micrometers, about 50 micrometers, about 60 micrometers, about 70micrometers, about 80 micrometers, about 90 micrometers, about 100micrometers, about 110 micrometers, about 120 micrometers, about 130micrometers, about 140 micrometers and about 150 micrometers.

In one preferred embodiment of the present invention, anode foil 65 hasa rated surge voltage of 390 Volts, an initial purity of about 99.99%aluminum, a final thickness of about 104 micrometers, plus or minusabout five micrometers, and a specific capacitance of about 0.8microfarads per square centimeter. Suitable anode foils for practicingthe present invention are commercially available on a widespread basis.

Cathode layers 175 are most preferably formed from cathode foil 70 (notshown in the Figures). Some preferred parameters of cathode foil havebeen discovered to include high surface area (i.e., highly etchedcathode foil), high specific capacitance (preferably at least 200microfarads/cm², and at least 250 microfarads/cm² when fresh), athickness of about 30 micrometers, a cleanliness of about 1.0 mg/m²respecting projected area maximum chloride contamination, and a puritywhich may be less than corresponding to the starting foil material fromwhich anode foil 65 is made.

In one preferred embodiment of the present invention, cathode foil 70has an initial purity of at least 99% aluminum, and more preferably yetof about 99.4% aluminum, a final thickness of about 30 micrometers, andan initial specific capacitance of about 250 microfarads per squarecentimeter.

In other embodiments of the present invention, cathode foil 70 has aspecific capacitance ranging between about 100 and about 500microfarads/cm², about 200 and about 400 microfarads/cm², or about 250and about 350 microfarads/cm², a thickness ranging between about 10 andabout 150 micrometers, about 15 and about 100 micrometers, about 20 andabout 50 micrometers, or about 25 and about 40 micrometers.

It is generally preferred that the specific capacitance of cathode foil70 be as high as possible, and that cathode layer 175 be as thin aspossible. For example, it is contemplated in the present invention thatindividual cathode layers 175 have specific capacitances of about 100microfarads/cm², about 200 microfarads/cm², about 300 microfarads/cm²,about 400 microfarads/cm², about 500 microfarads/cm², about 600microfarads/cm², about 700 microfarads/cm², about 800 microfarads/cm²,about 900 microfarads/cm², or about 1,000 microfarads/cm². Suitablecathode foils for practicing the present invention are commerciallyavailable on a widespread basis.

In still other embodiments of the present invention, cathode foil 70 isformed of materials or metals in addition to aluminum, aluminum alloysand "pure" aluminum.

Separator layers 180 are most preferably made from a roll or sheet ofseparator material 75. In one preferred embodiment, separator material75 is a pure cellulose, very low halide or chloride content Kraft paperhaving a thickness of about 0.0005 inches, a density of about 1.06grams/cm³, a dielectric strength of 1,400 ac Volts per 0.001 inchesthickness, and a low number of conducting paths (about 0.4 /ft² orless). Separator layers 180 are preferably cut slightly larger thananode layers 170 and cathode layers 175 to accommodate misalignmentduring the stacking of layers and to prevent subsequent shorting betweenelectrodes of opposite polarity.

It is preferred that separator layers 180 be formed of a material that:(a) is chemically inert; (b) is chemically compatible with the selectedelectrolyte; (c) may be impregnated with the electrolyte to produce alow resistance path between adjoining anode and cathode layers, and (d)physically separates adjoining anode and cathode layers. Separatorlayers 180 may also be formed of materials other than Kraft paper, suchas Manila paper, porous polymeric materials or fabric gauze materials.For example, porous polymeric materials may be disposed between anodeand cathode layers of like those disclosed in U.S. Pat. Nos. 3,555,369and 3,883,784 in some embodiments of the present invention.

In a preferred embodiment of the present invention, a liquid electrolytesaturates or wets separator layers 180 and is disposed within case 90.It is to be understood, however, that various embodiments of the presentinvention include within their scope a solid or adhesive electrolytesuch as those disclosed in U.S. Pat. Nos., 5,628,801; 5,584,890;4,942,501 and its continuations, U.S. Pat. Nos. 5,146,391 and 5,153,820.Note that in some embodiments of the present invention, an appropriateinter-electrode adhesives/electrolyte layer may be employed in place ofpaper, gauze or porous polymeric materials to form separator layer 180.

It will also be understood by those skilled in the art that there existmany different types and methods for making anode 65, cathode foil 70and separator material 75. What we disclose herein, therefore, are onlypreferred materials, methods and apparatus for making a preferredembodiment of capacitor 265 of the present invention, and its variouscomponents, and not all the materials, methods and apparatus suitablefor practicing the present invention and falling within the scopethereof.

Continuing to refer to FIG. 4, a first preferred step in assembling aflat aluminum electrolytic capacitor is to cut anode layers 185 and 190,anode tabs 195, cathode layers 175 and separator layers 180. Thosecomponents are most preferably cut to shape using dies having lowwall-to-wall clearance, where inter-wall spacing between thesubstantially vertically-oriented corresponding walls of the punch anddie is most preferably on the order of about 6 millionths of an inch perside. Larger or smaller inter-wall spacings between the substantiallyvertically-oriented corresponding walls of the punch and cavity, such asabout 2, about 4, about 5, about 7, about 8, about 10 and about 12millionths of an inch may also be employed in the present invention butare less preferred.

Such low clearance results in smooth, burr free edges being formed alongthe peripheries of anode layers 185 and 190, anode tabs 195, cathodelayers 175 and separator layers 180. Smooth, burr free edges on thewalls of the dies have been discovered to be critical respectingreliable performance of a capacitor.

The presence of burrs along the peripheries of anode layers 185 and 190,anode tabs 195, cathode layers 175 and separator layers 180 may resultin short circuit and failure of the capacitor. The means by which anodefoil, cathode foil and separator materials are cut or formed in thepresent invention may have a significant impact on the lack or presenceof burrs and other cutting debris disposed about the peripheries of theformed or cut members. We have found that the use of low clearance diesproduces an edge superior to that of other cutting methods, such assteel rule dies. The shape, flexibility and speed of a low clearance diehas been discovered to be superior to that of laser or blade cutting.

Other methods of cutting or forming anode layers 185 and 190, anode tabs195, cathode layers 175 and separator layers 180 falling within thescope of the present invention include, but are not limited to, steelrule die cutting, laser cutting, water jet cutting and blade cutting.

The preferred low clearance of the die apparatus of the presentinvention is especially important for cutting thin ductile materialssuch as cathode foil 70. In addition to improving reliability, burr anddebris reduction permits reductions in the thickness of separator layer180, thereby improving energy density of the capacitor. Angle cutting,where the face of the punch is not held parallel to the opposing floorof the die during the cutting step, is another less preferred method ofcutting or forming anode layers 185 and 190, anode tabs 195, cathodelayers 175 and separator layers 180 of the present invention.

It is preferred in the present invention to cut or otherwise formseparator layer 180 such that its outer periphery conforms closely tothat of the corresponding sidewalls of the interior of case 90. Inpreferred embodiments of the present invention, the periphery ofseparator layer is disposed within plus or minus 0.009 inches of thecorresponding sidewalls of case 90. Such close conformity between theperiphery of separator layer 180 and the corresponding internalsidewalls of case 90 has been discovered to provide the advantage ofpermitting separator layers 180 to immobilize or secure firmly in placeelectrode assembly 225 in case 90. This immobilization occurs becausethe separator paper forming separator layers 180 swells afterelectrolyte is added through fill port ferrule 105 into otherwiseassembled and sealed capacitor 265.

In a preferred method of the present invention, foil or separatormaterials are drawn between the punch and cavity portions of a diehaving appropriate clearances on a roll. An air or hydraulicallyactuated press is then most preferably employed to actuate the punch orcavity portion of the die. The punch portion of the die is mostpreferably formed of hardened tool steel, or has other suitable wearresistant materials or coatings disposed on the cutting surfacesthereof. When the cavity of the die is aligned vertically, the punchportion of the die may travel either upwards or downwards towards thedie cavity during a cutting cycle. In the former case, components arecut and drop downwardly into a container for use in subsequent assemblyoperations. In the latter case, components are cut and may be presenteddirectly to automated assembly equipment, such as robots equipped withvacuum or other pick-up tooling, for subsequent processing. Lowclearance dies of the type described herein may be supplied by Top Tool,Inc. of Minneapolis, Minn.

Anode sub-assembly 170 most preferably includes one notched anode layer190, which facilitates appropriate placement and positioning of anodetab 195 within anode sub-assembly 170. More than one notched anode layer190 may also be included in anode sub-assembly 170. It is preferred thatthe remaining anode layers of anode sub-assembly 170 be non-notchedanode layers 185. Anode tab 195 is most preferably formed of aluminumstrip material. In one preferred embodiment of the present invention,aluminum strip 80 has a purity of about 99.99% aluminum and a lesserdegree of anodization than anode foil 65. When anode tab 195 is formedof a non-anodized material, cold welding of anode tab 195 to non-notchedanode layers 185 may be accomplished with less force and deflection,more about which we say below. It is preferred that the thickness ofanode tab 195 be about equal to that of notched anode layer 190. If morethan one notched anode layer 190 is employed in anode sub-assembly 170,a thicker anode tab 195 may be employed.

FIG. 13 shows a flow chart that describes generally one method, frombeginning to end, of making flat aluminum electrolytic capacitor 265 ofthe present invention. FIGS. 14 through 20, on the other hand, showspecific portions of the method or process described generally in FIG.13.

FIG. 14 shows a flow chart of one method of the present invention formaking anode layer 170 of the present invention. In FIG. 14, non-notchedanode layers 185, notched anode layer 190 and anode tab 195 are providedand assembled within cold welder 202 to form anode sub-assembly 170.

Referring now to FIGS. 5(a) through 5(c), two non-notched anode layers185a and 185b are placed on cold welding fixture base layer 207 of coldwelding apparatus 202. The various structural members of cold weldingapparatus 202 are most preferably formed of precision machined stainlesssteel or a high strength aluminum alloy. Layers 185a and 185b are nextaligned and positioned appropriately on cold welding fixture base layer207 using spring loaded alignment pins 209a through 209e. Pins 209athrough 209e retract upon top layer 208 being pressed downwardly uponlayers 185a and 185b disposed within cold welding cavity 220. See alsoFIG. 5(c), where a cross-sectional view of cold welding apparatus 202 isshown.

Anode layer 190 is similarly disposed within cavity 220, followed byplacing anode tab 195 within anode tab notch 200 in notched anode layer190. Anode tab 195 is most preferably positioned along the periphery ofnotched anode layer 190 with the aid of additional spring loadedalignment pins 209f and 209g disposed along the periphery of anode tab195. Non-notched anode layer 185c is then placed atop anode layer 190.Stacked anode sub-assembly 170 is then clamped between top plate 208 andbase plate 207. Disposed within base plate 207 are anode layer coldwelding pins 206a and anode tab cold welding pin 211a. Disposed withintop plate 208 are anode layer cold welding pin 206b and anode tab coldwelding pin 211b. Base plate 207 and top plate 208 are aligned such thatthe axes of cold welding pins 206a and 206b coincide with and arealigned respecting corresponding cold welding pins 211a and 211b.

Upper actuation apparatus 214 of cold welding apparatus 202 displacescold welding pins 206b and 211b downwardly. Lower actuation apparatus215 displaces cold welding pins 206a and 211a upwardly. In oneembodiment of upper actuation apparatus 214 and lower actuationapparatus 215 of the present invention, pneumatic cylinders are employedto move pins 206a, 206b, 211a and 211b. In another embodiment ofapparatus 214 and apparatus 215 of the present invention, a pair ofrolling wheels is provided that move simultaneously and perpendicularlyto the axes of pins 206a, 206b, 211a, and 211b. Still other embodimentsof apparatus 214 and apparatus 215 of the present invention may employhydraulic actuators, cantilever beams, dead weights, springs,servomotors electromechanical solenoids, and the like for moving pins206a, 206b, 211a and 211b. Control of actuation apparatus 214 andapparatus 215 respecting pin displacement force magnitude and timing maybe accomplished using any one or combination of constant load, constantdisplacement, solenoid controller, direct or indirect means.

Following clamping with top plate 208, cold welding pins 206a, 206b,211a and 211b are actuated. Cold welds 205 and 210 in anode sub-assembly170 are formed by compression forces generated when cold weld pins 206a,206b, 211a and 211b are compressed thereagainst . See FIG. 6(a), wherethe preferred regions in which cold welds 205 and 210 are formed areshown. Cold welds 205 and 210 may be described as not only cold welds,but forged welds. This is because the interfacial boundaries betweenanode layers 185 are deformed in the region of welds 205 and 210,thereby disrupting oxide layers and bringing base metals into directcontact with one another where metallic bonding occurs. Metallic bondingincreases the strength of the welds.

In one embodiment of the method of the present invention, a plurality ofpneumatic cylinders function simultaneously in upper actuation apparatus214 and lower actuation apparatus 215 to drive pins 206a, 206b, 211a and211b against anode sub-assembly 170. Anode layer cold weld 205 and anodetab cold weld 210 are most preferably formed under direct constant loadconditions, where pneumatic cylinders are pressurized to a predeterminedfixed pressure. Anode layer cold weld 205 and anode tab cold weld 210may also be formed under indirect constant displacement conditions,where pneumatic cylinders are pressurized until a displacement sensorplaced across cold welding pins 206a, 206b, 211a or 211b generates asignal having a predetermined value, whereupon those pins are disengagedfrom sub-assembly 227.

In another embodiment of the method of the present invention, acantilever beam mechanism is incorporated into upper actuation apparatus214 and lower actuation apparatus 215. Anode layer cold weld 205 andanode tab cold weld 210 are formed under direct constant displacementconditions, where cantilever beams are actuated and cause upper andlower members 208 and 207 to engage sub-assembly 227 until a hard stoppoint is reached. An indirect load controlled system may also beemployed in apparatus 214 and apparatus 215, where cantilever or othermeans include a load measuring sensor for controlling the stop point ofthe cantilever beam, for example, when a predetermined load is measuredby the sensor.

The cross-sectional shape of cold weld pins 206a, 206b, 211a and 211bmay be square, circular, oval or any other suitable shape. The shape ofthe ends of cold weld pins 206a, 206b, 211a and 211b may be flat,rounded, domed or any other suitable shape appropriate for selectivelycontrolling the properties of the cold welds produced therein. Likewise,more or fewer than four cold weld pins may be employed in the presentinvention. The ends of cold weld pins 206a, 206b, 211a and 211b are mostpreferably rounded or domed and circular in cross-section. In apreferred embodiment of the present invention, cold weld pins 206a,206b, 211a and 211b have a diameter of about 0.060" and further have abeveled or radiused end. Cold weld pins 206a, 206b, 211a and 211b arepreferably made from a high strength material that does not readilydeform under the pressures obtained during welding, such as stainlesssteel, titanium, tool steel or HSLA steel. The ends or sidewalls of coldwelding pins 206a, 206b, 211a and 211b may be coated, cladded orotherwise modified to increase wear resistance, deformation resistanceor other desirable tribilogical attributes of the pins.

The primary function of cold welds 205 and 210 is to provide electricalinterconnections between layers 185a, 185b, 185c and 190 and anode tab195, while minimizing the overall thickness of anode sub-assembly 170 inthe regions of welds 205 and 210. We have discovered that typical priorart commercial cylindrical capacitors exhibit a significant increase inthe thickness of the anode layer in the regions of the cold welds. Thisincrease in thickness is typically on the order of about two times thethickness of the tab, or about 0.008 inches. In the case of cylindricalcapacitors where only one or two non-coincident tab connections arepresent, the overall effect on anode layer thickness may be minimal. Ina stacked layer design having many more interconnections and welds,however, increases in weld zone thickness have been found tosignificantly increase the overall thickness of the anode layer and thecapacitor.

In one method and corresponding apparatus of the present invention, noor an inappreciable net increase in anode sub-assembly 170 thicknessresults when cold weld geometries and formation processes areappropriately optimized. Several embodiments of anode-assembly 170 havebeen found to have no more than about a 20% increase in layer thicknessdue to the presence of cold welds, as compared to about a 200% increasein thickness resulting from cold welds found in some commercialcylindrical capacitors. In the present invention, two, three, four,five, six or more anode layers 185 and 190 may be cold-welded to formanode sub-assembly 170.

FIG. 6(b) shows a cross-sectional view of a portion of one embodiment ofa cold-welded anode assembly of the present invention. Anode layers185a, 190, 185b and 185c are cold-welded together at weld 205 throughthe compressive action of pins 206a and 206b mounted in bottom plate 207and top plate 208, respectively. Pins 206a and 206b form centraldepressions 293 and 294, respectively, in anode sub-assembly 170d, andfurther result in the formation of rims 295 and 296, respectively. Rims295 and 296 project downwardly and upwardly, respectively, from thesurrounding surfaces of anode subassembly 170d, thereby increasing theoverall thickness T of anode subassembly 170d by ΔT in respect of thenon-cold-welded surrounding regions or portions thereof.

FIG. 6(c) shows a cross-sectional view of another portion of oneembodiment of a cold-welded anode assembly of the present invention.Anode layers 185a, 185b, 185c and tab 195d are cold-welded together atweld 210 through the compressive action of pins 211a and 211b mounted inbottom plate 207 and top plate 208, respectively. Pins 211a and 211bform central depressions 297 and 298, respectively, in anodesub-assembly 170d, and further result in the formation of rims 299 and301, respectively. Rims 299 and 301 project downwardly and upwardly,respectively, from the surface of anode subassembly 170d, therebyincreasing overall thickness T of anode subassembly 170d by ΔT inrespect of the non-cold-welded regions thereof.

Anode subassembly 170d has a thickness defined by the equation:

    T=nt

where T is the overall thickness of anode subassembly 170d innon-cold-welded regions, n is the number of anode layers 185 and/or 190in anode subassembly 170d, and t is the thickness of individual anodelayers 185 and/or 190 or anode tab 195. The maximum overall thickness ofanode subassembly 170d in the region of cold welds 205 or 210 is thendefined by the equation:

    T+ΔT=nt+ΔT

We have discovered that it is highly desirable to form anode subassemblysuch that the ratio ΔT/T is less than or equal to 0.05, 0.1, 0.15, 0.20,0.25, 0.30, 0.35, 0.40, 0.45 or 0.50. The lower the value of the ratioΔT/T, the greater the volumetric efficiency of capacitor 265.Additionally, the overall thickness of capacitor 265 may be reduced whenthe value of the ratio ΔT/T is made smaller.

Referring now to FIG. 6(a), we have further discovered that the overallthickness of electrode assembly 225 may be reduced further by staggeringor offsetting horizontally the respective vertical locations of tabs195a through 195h (and corresponding cold welds 210). In this embodimentof the present invention, tabs 195a 195b, for example, are not alignedvertically in respect of one another. Such staggering or offsetting oftabs 195 permits the increases in thickness ΔT corresponding to each ofanode subassemblies 170a through 170h to be spread out horizontally overthe perimeter or other portion of electrode assembly 225 such thatincreases in thickness ΔT do not accumulate or add constructively,thereby decreasing the overall thickness of electrode assembly 225. Coldwelds 205 may similarly be staggered or offset horizontally respectingone another and cold weld 210 to achieve a reduction in overallthickness of electrode assembly 225.

In another embodiment of the present invention, anode sub-assembly 170comprises a plurality of three, four, five or more anode layers 185 and190, each sub-assembly most preferably having at least one anode layerhaving a corresponding anode tab 195 attached thereto or forming aportion thereof, the layers being cold welded together to form anodesub-assembly 170. For example, an anode sub-assembly 170 may comprisesix anode layers 185 constructed by cold-welding two separate tripleanode layers 185 that were previously and separately cold-welded orotherwise joined together. Alternatively, anode sub-assembly 170 layermay comprise seven anode layers constructed by cold-welding together onetriple anode layer 185 and one quadruple anode layer 185 that werepreviously and separately cold-welded or otherwise joined together. Inanother embodiment of the present invention, multiple notched anodelayers 190 may employed in anode sub-assembly 170, thereby permittingthe use of a thicker anode tab material 70.

The geometry of base plate 207 and top plate 208 in the regionssurrounding cold welding pins 206a, 206b, 211a and 211b has beendiscovered to affect the properties of cold welds 205 and 210. In apreferred method of the present invention, the mating surfaces of plates207 and 208 surfaces have no radiused break formed in the perimeters ofthe pin holes. We have found that the presence of radiused breaks orchamfers in those regions may cause undesired deformation of cold welds205 and 210 therein. Such deformation may result in an increase in thethickness of anode sub-assembly 170, which may translate directly intoan increase in the thickness of capacitor 265. Note further that theincrease in thickness so resulting is a multiple of the number of anodesub-assemblies 170 present in electrode assembly 225. In less preferredmethods of the present invention radiused breaks or chamfers may beemployed in the region of the pin holes in base plate 207 and top plate208, but appropriate capacitor design accommodations are most preferablymade, such as staggering the positions of adjoining stacked cold welds.

As shown in FIG. 14, once cold welding pins 206a, 206b, 211a and 211bhave been actuated against anode sub-assembly 170, top plate 208 isremoved and cold-welded anode sub-assembly 170 is provided for furtherstacking of electrode subassembly 227. FIG. 15 shows a flow chartcorresponding to one preferred method for making electrode assembly 225of the present invention. See also FIG. 6(a), where an exploded topperspective view of one embodiment of an electrode assembly 225 ofcapacitor 265 of the present invention is shown. As illustrated in FIGS.4, 6(a) and 15, electrode assembly 225 most preferably comprises aplurality of cold-welded anode sub-assemblies 175a through 175h, aplurality of cathode layers 175a through 175l, a plurality of separatorlayers 180, outer separator layers 165a and 165b, outer wrap 115 andwrapping tape 245.

Outer wrap 115 is most preferably die cut from separator material 75described supra, but may be formed from a wide range of other suitablematerials such as polymeric materials, aluminum, suitable heat shrinkmaterials, suitable rubberized materials and synthetic equivalents orderivatives thereof, and the like.

Wrapping tape 245 is most preferably cut from a polypropylene-backedacrylic adhesive tape, but may also be replaced by a staple, anultrasonic paper joint or weld, suitable adhesives other than acrylicadhesive, suitable tape other than polypropylene-backed tape, a hook andcorresponding clasp and so on.

Outer wrap 115 and wrapping tape 245 together comprise an electrodeassembly wrap which has been discovered to help prevent undesiredmovement or shifting of electrode assembly 225 during subsequentprocessing. It will now become apparent to one skilled in the art thatmany means other than those disclosed explicitly herein exist forimmobilizing and securing electrode assembly 225 during subsequentprocessing which accomplish substantially the same function as theelectrode assembly wrap comprising outer wrap 115 and wrapping tape 245.Alternative means for immobilizing and securing electrode assembly 225other than those described hereinabove exist. Such alternative meansinclude, but are not limited to, robotic or other mechanical clampingand securing means not necessarily forming a portion of electrodeassembly 225, adhesive electrolytes for forming separator layers 180,and so on.

The stacking process by which electrode assembly 225 is most preferablymade begins by placing outer wrap 115 into a stacking fixture followedby placing outer paper or separator layer 165a thereon. Next, cathodelayer 175a is placed atop separator layer 165a, followed by separatorlayers 180a and 180b being disposed thereon. Cold-welded anodesub-assembly 170a is then placed atop separator layer 180b, followed byplacing separator layers 180a and 180b thereon, and so on. The placementof alternating cathode layers 175 and anode layers 170 with separatorlayers 180a and 180b interposed therebetween continues in the stackingfixture until final cathode layer 175h has been placed thereon.

In the embodiment of electrode assembly 225 shown in FIG. 6(a), eightanode sub-assemblies (anode sub-assemblies 170a through 170h) and ninecathode layers (cathode layers 175a through 175i) are illustrated. Thevoltage developed across each combined anode sub-assembly/separatorlayer/cathode layer assembly disposed within electrode assembly 225 mostpreferably ranges between about 360 and about 390 Volts DC. As describedbelow, the various anode sub-assemblies of electrode assembly 225 aretypically connected in parallel electrically, as are the various cathodelayers of electrode assembly 225.

Consistent with the discussion hereinabove concerning FIG. 4, it willnow be understood by one skilled in the art that electrode assembly 225shown in FIG. 6(a) is merely illustrative, and does not limit the scopeof the present invention in any way respecting the number or combinationof anode sub-assemblies 170, cathode layers 175, separator layers 180,anode tabs 195, cathode tabs 176, and so on. The number of electrodecomponents is instead determined according to the total capacitancerequired, the total area of each layer, the specific capacitance of thefoil employed and other factors.

In another embodiment of electrode assembly 225 of the presentinvention, the number of anode layers 185 employed in each anodesub-assembly 170 is varied in the stack. Such a design permits thefabrication of capacitors having the same layer area but nearlycontinuously varying different and selectable total capacitances that auser may determine by increasing or decreasing the number of anodelayers 180 included in selected anode sub-assemblies 170 (as opposed toadding or subtracting full anode/cathode sub-assemblies 227 fromelectrode assembly 225 to thereby change the total capacitance).Following placement of cathode layer 175l in the stack, outer paperlayer 165b is placed thereon, and outer wrap 115 is folded over the topof electrode assembly 225. Wrapping tape 245 is then holds outer wrap115 in place and secures the various components of electrode assembly225 together.

The physical dimensions of separator layers 165 and 180 are mostpreferably somewhat larger than those of anode sub-assemblies 170 andcathode layers 175 to prevent contact of the electrodes with the casewall or electrical shorting between opposing polarity electrode layersdue to the presence of burrs, stray or particulate material, debris orimperfections occurring therein. The reliability and functionality ofcapacitor 265 are compromised if a portion of anode sub-assembly 170comes into contact with a conducting case wall, if a burr on theperiphery of anode sub-assembly 170 or cathode layer 175 comes intocontact with an adjoining layer of opposing polarity, or if separatorlayer 180a or 180b does not provide sufficient electrical insulationbetween adjoining opposite-polarity electrode layers and conductingparticulate matter bridges the gap therebetween.

The additional separator material most preferably disposed about theperiphery of electrode assembly 225 is referred to herein as separatoroverhang. Decreasing the amount of separator overhang increases theenergy density of capacitor 265. It is beneficial from an energy densityoptimization perspective, therefore, to decrease the amount or degree ofseparator overhang. The amount of separator overhang required has beendiscovered to be primarily a function of the stack-up tolerancecharacteristic of the stacking method employed.

In commercial cylindrical capacitors, we discovered that the amount ofseparator overhang is typically on the order of 0.050" to 0.100". Fayramet al. in the foregoing '851 patent describe a flat aluminumelectrolytic capacitor wherein the housing of the capacitor has at leasttwo internal alignment members. Those alignment members necessarily addvolume to the capacitor while taking away from the total amount of"active" electrode material available, thereby decreasing the energydensity of the capacitor.

We discovered a method of the present invention for assuring consistentregistration of separator layers 165 and 180, anode sub-assemblies 170and cathode layers 175 in electrode assembly 225: stacking the variouselements of electrode assembly 225 using robotic assembly techniques.More particularly, the various electrode and separator layers ofelectrode assembly 225 are stacked and aligned using an assemblyworkcell comprising four Seiko 4-axis SCARA Model No. TT8800 and TT8500,or equivalent, to pick up and place the various electrode and separatorelements in an appropriate stacking fixture. Other suitable methods ofthe present invention for stacking and registering electrode andseparator layers include cam driven walking beam assembly machinetechniques, rotary table machine techniques, multiple station singlestacking machine techniques, and the like.

In a preferred method of the present invention, a pre-formed or cutseparator, electrode layer or sub-assembly is presented to a robot arm,which then picks the part up with end-of-arm tooling. A Venturi systemproduces a vacuum in the end-of-arm tooling. The system creates a vacuumat an appropriate time such that the part is sucked up onto theend-of-arm tooling. The vacuum is next released when the part is placedin the stacking fixture. A direct vacuum system, such as rubber suctioncups, or other contact or non-contact pick up robotic or manual assemblymethods may also be employed in accordance with other methods of thepresent invention. The position of the part is robotically translatedfrom the pickup point into the stacking fixture by the robot arm with anaccuracy of 5 thousands of an inch or less. After placing the part inthe stacking fixture, part alignment is most preferably verifiedelectronically with a SEIKO COGNEX 5400 VISION System, or equivalent, incombination with a SONY XC-75 camera, or equivalent. The camera ismounted on the robot arm to permit the accuracy of part placement to beverified. This system can accurately determine the position of each partor element in electrode assembly 225 to within 0.01 millimeters. Onceall layers have been placed in the stacking fixture by the robot arm,the stack is presented for wrapping.

The foregoing methods of the present invention permit precise alignmentand stacking of separator layers 165 and 180, anode sub-assemblies 170and cathode layers 175 in electrode assembly 225, while minimizing theaddition of undesirable unused volume to capacitor 265.

We discovered another method for assuring registration of separatorlayers 165 and 180, anode sub-assembly 170 and cathode layer 175 inelectrode assembly 225, wherein alignment elements disposed within thestacking fixture are employed in a manual process which utilizes fixtureregistration points. In such a method, the stacking fixture has severalalignment elements such as posts or sidewalls disposed about itsperiphery for positioning separator layers 165 and 180. Because cathodelayers 175 and anode sub-assemblies 170 do not extend to the peripheryof the separator, an alternative means for accurately positioning thoseelectrodes becomes necessary.

Positioning of alternating cathode layers 175 and anode sub-assemblies170 is most preferably accomplished using alignment elements such asposts or sidewalls disposed about the periphery of cathode tab 176 andanode tab 195. It has been discovered that the accuracy of layerplacement and positioning is primarily a function of the length of theelectrode tabs. The longer the tab, the less significant the alignmenterror becomes. Electrode tab length must typically be balanced againstthe loss of electrode material which occurs during die cutting, which inturn results primarily due to the longer length of cathode tab 176 inrespect of the length of anode tab 195. Tabs 176 and 195 may include orcontain alignment features therein having any suitable geometry forfacilitating registration and positioning in respect of alignmentelements: Any additional tab length utilized for registration of theelectrode layers is most preferably trimmed from electrode assembly 225during the process of electrode tab interconnection (more about which wesay below).

Another method of the present invention for ensuring registration ofseparator layers 165 and 180, anode sub-assembly 170 and cathode layer175 in electrode assembly 225 which does not require the use of internalalignment elements within capacitor 265 is enveloping or covering anodesub-assembly 170 and cathode layer 175 with separator material. In thismethod of the present invention, separator layers 180a and 180b arecombined into a single die cut piece part that is folded around eitheranode sub-assembly 170 or cathode layer 175. The free edges of theseparator are then secured by doubled-sided transfer tape, anotheradhesive, stitching or ultrasonic paper welding. Construction of anelectrode subassembly in this manner secures and registers anodesub-assembly 170 and cathode layer 175 in respect of the periphery ofthe separator envelope so formed. The resulting electrode subassembly227 is then presented for stacking in electrode assembly 225.

Yet another method of the present invention we have found for securingthe separator to anode sub-assembly 170 is through the use of pressurebonding techniques. In such a method, separator layer 165 or 180 ispressed into a surface of anode sub-assembly 170 or anode layer 185 overa localized region thereof with sufficient force to rigidly affix theseparator paper to anode sub-assembly 170, but not with such great forcethat a portion of underlying anode sub-assembly 170 is fractured. Othermethods of securing all or portions of separator layer 165 or 180 toanode sub-assembly 170 or anode layer 185 include, but are not limitedto, stitching, adhesive bonding and ultrasonic paper welding techniques.

FIG. 7 shows a top perspective view of one embodiment of an electrodeassembly of a capacitor of the present invention. FIG. 8 shows anenlarged view of a portion of the electrode assembly of FIG. 7. Afterwrapping electrode assembly 225 with outer wrap 115 and wrapping tape245, interconnection of anode tabs 232 and cathode tabs 233 with theirrespective external terminals is most preferably made.

FIG. 9 shows an exploded top perspective view of one embodiment of acapacitor of the present invention employing the electrode assembly ofFIGS. 6, 7 and 8 therein. This embodiment of the present inventionincludes anode feedthrough 120 and cathode feedthrough 125 mostpreferably having coiled basal portions 121 and 126, respectively.Feedthroughs 120 and 125 provide electrical feedthrough terminals forcapacitor 265 and gather anode tabs 232 and cathode tabs 233 withinbasal portions 121 and 126 for electrical and mechanicalinterconnection.

FIG. 16 shows a flow chart corresponding to one method of making tabinterconnections and feedthrough terminal connections of the presentinvention. In such a method, feedthrough wire is first provided forconstruction of feedthroughs 120 and 125, as shown in FIGS. 9 and 10. Inone embodiment of the present invention, a preferred feedthrough wire isaluminum having a purity greater than or equal to 99.99% and a diameterof 0.020 inches. Wire is trimmed to predetermined lengths for use inanode feedthrough 120 or cathode feedthrough 125. One end of the trimmedwire is coiled such that its inside diameter or dimension is slightlylarger than the diameter or dimension required to encircle gatheredanode tabs 232 or gathered cathode tabs 233.

Anode tabs 232 are next gathered, or brought together in a bundle bycrimping, and inside diameter 131 of anode feedthrough coil assembly 120is placed over anode tabs 232 such that anode feedthrough pin 130extends outwardly away from the base of anode tabs 232. Similarly,cathode tabs 233 are gathered and inside diameter 136 of cathodefeedthrough coil assembly 125 is placed over cathode tabs 233 such thatcathode feedthrough pin 135 extends outwardly away from the base ofcathode tab 233. Coiled basal portions 121 and 126 of anode and cathodefeedthroughs 120 and 125 are then most preferably crimped onto anode andcathode tabs 232 and 233, followed by trimming the distal ends thereof,most preferably such that the crimps so formed are orientedsubstantially perpendicular to imaginary axes 234 and 235 of tabs 232and 233. Trimming the distal ends may also, but less preferably, beaccomplished at other non-perpendicular angles respecting imaginary axes234 and 235.

In some methods of the present invention, a crimping force is applied tofeedthrough coils 130 and 135 and tabs 232 and 233 throughout asubsequent preferred welding step. In one method of the presentinvention, it is preferred that the crimped anode and cathodefeedthroughs be laser or ultrasonically welded along the top portion ofthe trimmed edge of the distal ends to anode and cathode tabs 232 and233.

Following welding of feedthroughs 120 and 125 to anode tabs 232 andcathode tabs 233, respectively, pins 130 and 135 are bent to insertionthrough feedthrough holes 142 and 143 of case 90.

Many different embodiments of the feedthroughs, and means for connectingthe feedthroughs, of the present invention to anode and cathode tabsexist other than those shown explicitly in the Figures. For example,feedthroughs of the present invention include within their scopeembodiments comprising basal portions having open sides, forming "U" or"T" shapes in cross-section, forming a coil having a single turn ofwire, forming a coil having three or more turns of wire, formed fromflattened wire, or basal portions formed from crimping sleeves or layersof metal for connecting feedthrough pins 130 and 135 to anode andcathode tabs 232 and 233.

FIG. 17 shows a flow chart corresponding to one method of the presentinvention for making tab interconnections and feedthrough connections.In this method, anode feedthrough 120 and cathode feedthrough 125 haveno coiled portions. Anode tabs 232 and cathode tabs 233 are gathered andtrimmed, followed by the basal portions of anode and cathodefeedthroughs 120 and 125 being placed propinquant to anode tabs 232 andcathode tabs 233, respectively. The basal portions of feedthroughs 120and 125 are then joined to anode tabs 232 and cathode tabs 233,respectively, most preferably by ultrasonic welding means.

In yet another method of the present invention, the basal portions offeedthroughs 120 and 125 are flattened to facilitate welding to anodeand cathode tabs 232 and 233. In still another method of the presentinvention, the basal portions of feedthrough pins 130 and 135 are formedsuch that they engage anode tabs 232 or cathode tabs 233 around theperiphery of the tabs by means other than coiling. For example, basalportions 121 and 126 of feedthroughs 120 and 125 may be "flag shaped,"and the flag portions thereof may be wrapped around tabs 232 and 233. Inyet other methods of the present invention, feedthrough pins 130 and 135may be attached to anode and cathode tabs 232 and 233 with resistancewelds, cold welds, brazing, friction welds, or an additional feedthroughcomponent such as a crimping sleeve may capture and join tabs 232 and233 for providing electrical and mechanical connections thereto.

It has been discovered that the processes of forming electricalconnections between tabs 232 and 233 and feedthrough coil assemblies 120and 125 can introduce undesirable stress on tabs 176 and 195. Theresultant strain induced in those tabs has further been found tomanifest itself as tears in cathode layer 175 at the base of cathode tab176, or as fractures in relatively low strength cold welds 205 or 210within anode sub-assembly 170. One advantage of the coiled portions offeedthroughs 120 and 125 is that they can provide strain relief betweenfeedthrough pins 130 and 135 and tabs 232 and 233. Thus, the strainrelief features of feedthroughs 120 and 125 help minimize or eliminateundesirable stress in feedthrough connections.

The foregoing means for connecting multiple electrode tab elements is tofeedthroughs may also be employed in other energy storage devices suchas batteries, electrochemical cells and cylindrically wound capacitors.

As employed in the specification and claims hereof, the term "laserwelding" means, but is not necessarily limited to, a method of weldingwherein coherent light beam processing is employed. Other means ofcoherent light beam processing falling within the scope of the method ofthe present invention include electron beam or laser welding methods(e.g., Nd:YAG, CO₂ processes) having hard or fiber optic beam deliveryin pulsed, continuous, or q-switched modes. Still other welding meansfall within the scope of the method of the present invention, such asmicro metal inert gas welding and micro plasma welding processes.

Table 2 sets forth optimized, preferred processing parameters we havediscovered under which various components of capacitor 265 are laserwelded to one another. The parameters set forth in Table 2 correspond tothose for a Model No. JK702H pulsed Nd:YAG laser welding system havinghard optic beam delivery manufactured by Lumonics Laserdyne of EdenPrairie, Minn.

Table 3 sets forth a range of parameters under which the same type oflaser welding system provides acceptable weld characteristics inaccordance with other methods of the present invention.

                  TABLE 2                                                         ______________________________________                                        Optimized Nd:YAG Laser Welding Parameters                                               Optimized Laser Welding Parameters*                                             Energy                                                                                                   Feed   per                                                                           Argon                                                 Pulse       Rate        Pulse                                                                  Pulse                                                                           Cover                                                    Frequency                (Joules/                                                       (inches/                                                                           Width Gas                                  Weld Type             (Hertz)     pulse)                                                                      min)                                                                                 (msec)                                                                           (SCFH)                              ______________________________________                                         Feedthrough Ferrule to                                                                   13.5    4.5      3     5     35                                   Case Tack 1                                                                   Feedthrough Ferrule to                                                                         9.75                                                                                20                   35                                Case Weld                                                                     Fillport Ferrule to                                                                              13.5                                                                              4.5         3                                                                                        35                              Case Tack 1                                                                   Fillport Ferrule to                                                                              15                                                                                 15         2                                                                                        35                              Case Weld                                                                     Anode Feedthrough                                                                                       10                  35                              Tabs                                                                          Cathode Feedthrough                                                                              4                                                                                    10          5           35                          Tabs                                                                          Cover to Case                                                                                         40                  60                                Filltube Sea                                                                                         15                     30                              ______________________________________                                         Lumonics JK702H Nd:YAG laser having an initial beam diameter of               approximately one inch passing through a final focusing lens with a 146 m     focal length (purchased having "160 mm lens", actual fine focal point         measured was 146 mm) and a spot size at the joint surface of 0.022 inches     The cover gas was coaxial. It will be understood that variations              respecting the manufacturer of the laser, beam delivery optics,  # the        initial beam size final focusing lens, spot size of the beam and the like     fall within the scope of a method of the present invention.              

                  TABLE 3                                                         ______________________________________                                        Generalized Nd:YAG Laser Welding Parameters                                             Generalized Laser Welding Parameters*                                           Energy                                                                                                   Feed   per                                                                               Argon                                             Pulse       Rate        Pulse                                                                  Pulse                                                                           Cover                                                    Frequency                 (Joules/                                                      (inches/                                                                           Width Gas                                  Weld Type             (Hertz)     pulse)                                                                      min)                                                                              (msec)                                                                              (SCFH)                              ______________________________________                                         Feedthrough Ferrule to                                                                   2-15    3-30     1-5   3.5-8 30-60                                Case                                                                          Fillport Ferrule to                                                                           2-15                                                                                   3-30                                                                                 1-5                                                                                   3.5-8                                                                            30-60                              Case                                                                          Feedthrough Tabs                                                                                       1-20                                                                                 1-7                                                                                   3.5-8                                                                            30-60                              Cover to Case                                                                                      10-40 5-25                                                                               1-7                                                                                   3.5-8                                                                            30-60                              Filltube Seal                                                                                          5- 200                                                                               1-10                                                                             3.5-8   30- 60                             ______________________________________                                         Lumonics JK702H Nd:YAG laser having an initial beam diameter of               approximately one inch passing through a final focusing lens with a 146 m     focal length (purchased having "160 mm lens", actual fine focal point         measured was 146 mm) and a spot size at the joint surface of 0.022 inches     The cover gas was coaxial. It will be understood that variations              respecting the manufacturer of the laser, beam delivery optics, the           initial beam size  # final focusing lens, spot size of the beam and the       like fall within the scope of a method of the present invention.         

FIG. 10 shows an exploded top perspective view of capacitor 265 of FIG.9 in a partially assembled state. FIG. 18 shows a flow chart of onemethod of making case subassembly 108. Case 90, anode ferrule 95,cathode ferrule 100, and fill port ferrule 105 are first provided. Case90 contains a means for accepting anode ferrule 95 therein, shown inFIGS. 9 and 10 as anode feedthrough ferrule hole 142. Case 90 furthercontains a means for accepting cathode ferrule 100, shown in FIGS. 9 and10 as cathode feedthrough ferrule hole 143. Case 90 also includes ameans for accepting fill port ferrule 105, shown in FIGS. 9 and 10 asfill port hole 106. In a preferred embodiment of the present invention,case 90 and cover 110 are formed of aluminum. In other embodiments ofthe present invention, case 90 or cover 110 may be formed of any othersuitable corrosion-resistant metal such as titanium or stainless steel,or may alternatively be formed of a suitable plastic, polymeric materialor ceramic.

Case 90, cover 110 and capacitor 265 of the present invention mayadditionally form a case negative capacitor (where can 90 and cover 110are electrically connected to the cathode layers, and where can 90 andcover 110 are at the same electrical potential as the cathode layers,i.e., at negative potential), or a floating case capacitor (where can 90and cover 110 are electrically connected neither to the cathode layersnor to the anode sub-assemblies, and where can 90 and cover 110 are atsubstantially no electrical potential or at an electrical potential thatfloats with respect to the respective potentials of the cathode layersand the anode sub-assemblies). In some embodiments of the presentinvention, case 90 or cover 110 may be formed of an electricallynon-conductive material or substantially electrically non-conductivematerial such as a suitable plastic, polymeric or ceramic material.

Ferrules 95, 100 and 105 are most preferably welded to case 90 (orotherwise attached thereto such as by a suitable epoxy, adhesive,solder, glue or the like), and together comprise case subassembly 108.Radial flanges in anode ferrule 95 and cathode ferrule 100 provide aregion for making a lap joint between the side wall of case 90 andaround the perimeters of feedthrough ferrule holes 142 and 143. Inpreferred methods of the present invention, a circumferential laser weldis disposed in joint 93, and welding is carried out in two primarysteps. First, a series of tack welds is made around the circumference ofjoint 93. The tack welds are most preferably made either by makingadjoining, successive tack welds around the perimeter or by making afirst tack weld at a first location along the perimeter, making a secondweld diametrically opposed from the first weld along the perimeter,making a third weld adjacent to the first weld, making a fourth weldadjacent to the second weld, and so on. Finally, a final closing weld ismade around the hole perimeter to hermetically seal tack welded joint93.

Table 2 sets forth an optimized set of parameters under which anodeferrule 95 and cathode ferrule 100 are joined to case 90. Table 3 setsforth a range of general parameters under which the same laser weldingsystem provides acceptable weld characteristics for joining anodeferrule 95 and cathode ferrule 100 to case 90.

FIG. 18 shows steps for inserting anode wire guide 140 into the insidediameter of anode ferrule 95, and inserting cathode wire guide 141 intothe inside diameter of cathode ferrule 100. Wire guides 140 and 141center pins within the inside diameter of the ferrules to permit anodeand cathode pins 130 and 135 to be electrically insulated from theinside surface of case 90, anode ferrule 95, and cathode ferrule 100.Wire guides 140 and 141 may themselves be electrically insulative, andelectrical insulation of pins 130 and 135 from case 90 and othercomponents is most preferably enhanced by means of potting adhesive 160.FIG. 20 shows further details concerning one method of the presentinvention for forming electrical insulation between pins 130 and 135 andanode ferrule 95 and cathode ferrule 100.

Wire guides 140 and 141 most preferably contain annular, ramped, or"snap-in" features formed integrally therein. Those features preventwire guides 140 and 141 from being pushed out of their respectiveferrules during handling, but are most preferably formed such thatinsertion of wire guides 140 and 141 in their corresponding ferrules mayoccur using forces sufficiently low so as not to damage case 90 orferrules 95 or 100 during the inserting step.

Wire guides 140 and 141 may be formed from any of a wide variety ofelectrically insulative materials that are stable in the environment ofan electrolytic capacitor. In one preferred embodiment of the presentinvention, the material from which wire guides 140 and 141 is made is aninjection molded polysulfone known as AMOCO UDEL supplied by AmocoPerformance Products of Atlanta, Ga. In other embodiments of the presentinvention, wire guides 140 and 141 may be formed from other chemicallyresistant polymers such as fluoroplastics (e.g., ETFE, PTFE, ECTFE,PCTFE, FEP, PFA or PVDF), fluoroelastomers, polyesters, polyamides,polyethylenes, polypropylenes, polyacetals, polyetherketones,polyarylketones, polyether sulfones, polyphenyl sulfones, polysulfones,polyarylsulfones, polyetherimides, polyimides, poly(amide-imides), PVC,PVDC-PVC copolymers, CPVC, polyfurans, poly(phenylene sulfides), epoxyresins, silicone elastomers, nitrile rubbers, chloroprene polymers,chlorosulfonated rubbers, polysulfide rubbers, ethylene-polypropyleneelastomers, butyl rubbers, polyacrylic rubbers, fiber-reinforcedplastics, glass, ceramic and other suitable electrically insulative,chemically compatible materials.

As used in the specification and claims hereof, the foregoing acronymshave the following meanings: the acronym "ETFE" meanspoly(ethylene-co-tetrafluoroethylene); the acronym "PTFE" meanspolytetrafluoroethylene; the acronym "CTFE" meanspoly(ethylene-co-chlorotrifluoroethylene); the acronym "PCTFE" meanspolychlorotrifluoroethylene; the acronym "FEP" means fluorinatedethylene-propylene copolymer; the acronym "PFA" perfluoroalkoxyfluoropolymer; the acronym "PVDF" means polyvinylidene fluoride; theacronym "PVC" means polyvinyl chloride; the acronym "PVDC-PVC" meanspolyvinylidene chloride--polyvinyl chloride copolymer; and the acronym"CPVC" means chlorinated polyvinyl chloride.

FIG. 11 shows a top view of one embodiment of assembled capacitor 265 ofthe present invention with cover 110 not present. Electrode assembly 225has been inserted into case subassembly 108 through wire guides 140 and141. In one embodiment of the present invention, the headspace portionof electrode assembly 225 (referred to herein as headspace 230) isinsulated from case 90 and cover 110. The means of the present inventionby which headspace insulation may be provided include molded,thermally-formed, die cut, or mechanically formed insulating materialsand means, where the materials and means are stable in the environmentof an electrolytic capacitor. Suitable materials from which headspaceinsulators may be formed include all those listed hereinabove respectingmaterials for forming wire guides 140 and 141. Another means ofproviding headspace insulation is to wrap electrically insulative tape,similar to wrapping tape 245, around headspace 230 to prevent the anodeor cathode terminals from contacting case 90 or cover 110.

FIGS. 26(a) through 26(p) show different embodiments of joint 93 and thecrimp of the present invention. Various types of crimp and jointconfigurations for joining the cover 110 to case 90 are illustrated incross-section in those figures.

The inventors of the present invention have discovered that theparticular structural configuration of joint 93 is of the utmostimportance in respect of the suitable laser weldability thereof. Moreparticularly, it has been discovered that joints for covers of prior artflat capacitors having metal cases and covers and conventional jointstructures generally permit laser energy to enter the interior ofcapacitor 265 through the joints formed between the covers and casesthereof, thereby damaging or heating up components disposed inside case90. Joints of the prior art which permit such undesired penetration oflaser energy inside capacitor 265 were discovered to generally have acommon feature: a joint geometry wherein a straight or substantiallystraight line of sight or portion existed or was disposed through thejoint between the interior of the capacitor and the exterior of thecapacitor. Joints having no such straight line of sight or portionthrough the joint between the exterior and interior of the capacitorwere found to eliminate or at least diminish substantially the illeffects attending laser energy penetration to the interior of thecapacitor.

In one embodiment of the present invention, case 90, cover 110, joint93, upper edge 94, raised portion 95, stepped portion 96, groove 97,stepped portion 98 and outer edge 111 cooperate with one another tocause laser energy entering joint 93 from the exterior of capacitor 265to be reflected or scattered to the outside of capacitor 265, andfurther to be contained or absorbed within joint 93 in such a mannerthat no or substantially no laser energy penetrates joint 93 and entersthe interior of capacitor 265 while simultaneously forming a suitableweld in joint 93 between case 90 and cover 110. This absorption,containment, backscattering or reflecting of laser energy by joint 93results at least partially from the multiple orientations of joint 93 asit wends its way from the exterior of capacitor 265 to the interiorthereof. In other words, and as illustrated in FIGS. 26(a) through26(p), joint 93 of the present invention has multiple portions that arebent, non-parallel or serpentine respecting one another.

In one method of the present invention for laser welding joint 93, anaxis of a laser beam is directed inwardly along or parallel to thesurfaces defining a first portion of joint 93 (e.g., parallel toimaginary axis 102 or imaginary axis 101, depending on the particularembodiment of the present invention at hand). Upon entering the firstportion of joint 93 or a region propinquant thereto, the laser beamencounters at least a second portion of joint 93 defined by surfacesthat are bent or not parallel respecting the surfaces defining the firstportion of joint 93. As shown in FIGS. 26(e) through 26(h) and 26(m)through 26(p), joint 93 of the present invention may also have a thirdportion defined by surfaces that are bent or non-parallel respecting thesurfaces defining the second portion of joint 93. Consequently, andproviding appropriate parameters are selected by a user for operatingthe laser welding system of the present invention, no portion of thelaser beam impinging upon the first portion of joint 93 may penetratejoint 93 sufficiently far such that the laser beam reaches the interiorof capacitor 265 without first being absorbed, reflected or scattered.

In another method of the present invention for laser welding joint 93,an axis of a laser beam is directed inwardly along or parallel to thesurfaces defining a second portion of joint 93 (e.g., parallel toimaginary axis 102 or imaginary axis 101, depending on the particularembodiment of the present invention at hand). Upon entering the secondportion of joint 93 or a region propinquant thereto, the laser beamencounters at least a first or third portion of joint 93 defined bysurfaces that are bent or not parallel respecting the surfaces definingthe second portion of joint 93.

FIGS. 26(a) through 26(d) show a first embodiment of joint 93 and thecrimp of the present invention, wherein case 90 has inner and outersidewalls 91 and 92 extending upwardly from a flat planar base of case90 to form an open end that terminates in upper edge 94 disposed betweeninner and outer sidewalls 91 and 92. Upper edge 94 most preferablycomprises at least one stepped portion 96 and at least one raisedportion 95. Substantially planar cover 110 seals the open end of thecase, cover 110 having upper and lower surfaces 112 and 113,respectively, separated by outer edge 111. At least portions of outeredge 111 are shaped to engage at least one stepped portion 96 of upperedge 94 such that cover 110 self-registers on case 90 when cover 110 isdisposed over the open end of case 90, outer edge 111 is alignedapproximately upper edge 94, and cover 90 is placed thereon.

As shown in FIGS. 26(a) and 26(c), at least one raised portion 95 ofupper edge 94 initially extends above upper surface 112 of cover 110when at least portions of outer edge 111 are placed on and engage atleast one stepped portion 96. As shown in FIGS. 26(b) and 26(d), atleast one raised portion 95 is crimped or folded inwardly over or alongupper surface 112 of cover 110 to form joint 93 after at least portionsof outer edge 111 are placed on and engage the least one stepped portion96. Next joint 93 is laser welded to hermetically seal cover 110 to case90.

In the laser welding step, the laser beam may be directed substantiallyparallel to axes 101 and 102 of FIG. 26(b) to form a weld in the firstor second portions of joint 93. Alternatively, the laser beam may bedirected substantially parallel to axis 101 of FIG. 26(a) (i.e.,substantially parallel to upstanding sidewalls 91 and 92) after raisedportion 95 is crimped over cover 110 such that at least portions ofraised portion 95 melt and thereby weld first, second, third or otherportions of joint 93 closed. Our laser welding method invention includeswithin its scope laser welding steps where the laser beam is oriented indirections other than those set forth explicitly above.

In FIGS. 26(a) and 26(c), imaginary axes 101 and 102 are oriented at anangle theta of about 90 degrees respecting one another, where imaginaryaxis 101 defines the initial orientation of upper edge 94 and imaginaryaxis 102 defines the orientation of the plane within which cover 110 isdisposed. In FIGS. 26(b) and 26(d), after upper edge 94 has been crimpedor folded inwardly over or along upper surface, imaginary axis 101 isoriented at an angle theta of about 0 degrees respecting imaginary axis102.

FIGS. 26(e) through 26(f) show a second embodiment of the crimp andjoint 93 of the present invention, where case 90 has inner and outersidewalls 91 and 92, respectively, extending upwardly from a flat planarbase of case 90 to form an open end terminating in upper edge 94disposed between inner and outer sidewalls 91 and 92. Substantiallyplanar cover 110 seals the open end of case 90. Cover 110 comprisesupper and lower surfaces 112 and 113, respectively, separated by outeredge 111. Lower surface 113 of cover 110 has disposed thereon at leastone of groove 97 (see FIGS. 26(e) and 26(f)) and stepped portion 98 (seeFIGS. 26(g) and 26(h)). Groove 97 or stepped portion 98 is disposedradially inward from outer edge 111.

At least portions of groove 97 or stepped portion 98 are shaped toengage corresponding portions of upper edge 94 such that groove 97 orstepped portion 98, in combination with upper edge 94, cause cover 110to self-register on upper edge 94 when cover 110 is disposed over theopen end of case 90, groove 97 or stepped portion 98 is alignedapproximately with upper edge 94, and cover 110 is placed on upper edge94. Outer portions 117 of cover 110 extending between outer edge 111 andgroove 97 or stepped portion 98 are crimped or folded downwardly over atleast portions of outer sidewall 92 of case 90 to form joint 93 aftercover 110 is placed on the open end of can 90. Joint 93 is laser weldedto hermetically seal cover 110 to case 90.

In the laser welding step, the laser beam may be directed substantiallyparallel to axes 101 and 102 of FIG. 26(f) to form a weld in the first,second or other portions of joint 93. Alternatively, the laser beam maybe directed substantially parallel to axis 102 of FIGS. 26(e) or 26(g)(i.e., substantially parallel to the plane forming cover 110) afterouter portion of cover 110 is crimped over outer sidewall 92 such thatat least portions of outer portions of cover 110 melt and thereby weldfirst, second, third or other portions of joint 93 closed. Our laserwelding method invention includes within its scope laser welding stepswhere the laser beam is oriented in directions other than those setforth explicitly above.

In FIGS. 26(e) and 26(g), imaginary axes 101 and 102 are initiallyoriented at an angle theta of about 90 degrees respecting one another,where imaginary axis 101 defines the orientation of upper edge 94 andimaginary axis 102 defines the initial orientation of outer edge 111. InFIGS. 26(f) and 26(h), after outer edge 111 has been crimped or foldeddownwardly over at least portions of outer sidewall 92, imaginary axis102 is oriented at an angle theta of about 0 degrees respectingimaginary axis 102.

FIGS. 26(i) through 26(p) show yet other embodiments of the crimp andjoint of the present invention, where the angle theta defining theorientations of imaginary axes 101 and 102 respecting one another afterupper edge 94 has been crimped or folded inwardly, or outer edge 111 hasbeen crimped or folded downwardly, is greater than or equal to 0 degreesbut less than 90 degrees. The embodiments of the present invention shownin FIGS. 26(i) through 26(p) have been discovered to be particularlyefficacious for providing good access to joint 93 for a laser weldingbeam.

Note, however, that many variations of the particular cover, case andjoint geometries disclosed explicitly herein are possible and fallwithin the scope of the apparatus and corresponding methods of thepresent invention. For example, the case and cover of the presentinvention may form two aluminum-containing half-cases having upwardlyand downwardly extending sidewalls, the two half-cases forming two openends that are subsequently laser welded together. Alternatively, thecase and cover may form two substantially planar aluminum-containingmembers separated by a single or multiple sidewall members, the twoplanar members being laser welded to the intervening sidewall members.

FIGS. 26(a) through 26(p) also show registration marks or alignmentfeatures 99 disposed on case 90 or cover 110. Registration mark oralignment feature 99 is employed to establish a reference position injoint 93 for the welding apparatus after the case or cover has beencrimped or folded, thereby ensuring precise position of the weldingapparatus in respect of case 90, cover 110 and joint 93 when a weld isbeing formed in joint 93. It has been discovered that optimum resultsare obtained when registration mark 99 is disposed on upper surface 112of cover 110.

FIG. 19 shows a flow chart according to one method of the presentinvention for sealing case 90 and cover 110. Case subassembly 108 isprovided with electrode assembly 225 inserted in case 90. Cover 110 isdisposed atop upper edge 94 formed in case 90. In one method of thepresent invention, raised portion 95 of upper edge 94 extends about0.014" above upper surface 112 of cover 110 when cover 110 is placed onupper edge 94. The assembly is placed within a crimping mechanism ornest, and a clamp is actuated to hold cover 110 against upper edge 94and stepped portion 96. The crimping mechanism is actuated to crimp orfold over inwardly raised portion 95 onto, along or over upper surface112 of cover 110.

In another method of the present invention, crimping of raised portion95 is accomplished using a die cut to the shape of case 90 and furtherhaving angled or ramped sidewalls for engaging and pressing inwardlyraised portion 95 over upper surface 112 of cover 110. A crimp may alsobe formed with a moving crimp apparatus that travels around theperimeter of case 90 while continuously crimping raised portion 95 overupper surface 112 of cover 110. The foregoing methods may be readilyadapted to permit the crimping or folding of edge 111 of cover 110downwardly over outer sidewall 92.

Crimping of raised portion 95 onto cover 110 or outer edge 111 ontosidewall 92 provides several advantages. First, laser welding of cover110 to case 90 may be accomplished using relatively simple tooling,thereby resulting in short process times. Laser welding often provides abottleneck in manufacturing process flow when components such as case 90and cover 110 typically must be aligned precisely respecting oneanother. The elimination of such alignment steps during the laserwelding process has been discovered to help eliminate manufacturingprocess bottlenecks. Folding or crimping raised portion 95 or outer edge111 prevents a laser beam from entering the interior of capacitor 265.Instead, a laser beam is forced to couple with the material of case 90and cover 110 to thereby induce melting. It was discovered that joints93 not having crimps forming at least a portion thereof may permit alaser beam to damage components inside capacitor 265.

Another advantage of the crimped joint of the present invention is thatthe crimp provides additional metal in the weld zone. Aluminum, having ahigh thermal expansion coefficient, is sensitive to cracking upon rapidcooling from the high temperatures characteristic of welding processes.We discovered that the additional metal provided by the crimp decreasescracking sensitivity in joint 93. Joint 93 of the present invention isformed such that imaginary axes 101 and 102 are oriented at an angletheta respecting one another where theta is less than 90 degrees butgreater than or equal to 0 degrees. It is notable that crimping of case90 and cover 110 to one another helps registration of case 90 and cover110 in respect of one another prior to the welding of at least portionsof joint 93 being undertaken.

Crimped case 90 and cover 110 are next removed from the crimp fixtureand placed in a welding fixture. A laser weld is made in joint 93 tohermetically seal case 90 to cover 110. Table 2 sets forth an optimizedset of parameters under which the crimped case/cover joint may be sealedusing a pulsed Nd:YAG laser welding system. Table 3 sets forth ageneralized range of conditions under which the same laser weldingsystem provides acceptable results.

In a preferred method of the present invention, machined, stamped,etched or otherwise-formed registration marks or alignment features 99are disposed on cover 110 or case 90 to permit the relative positions ofcover 110 and case 90 to be determined precisely for the laser weldingstep. Connectors are then attached to the welded case/electrodeassembly.

FIG. 20 shows a flow chart according to one method of the presentinvention for sealing anode feedthrough portion 235 and cathodefeedthrough portion 240 of capacitor 265. See also FIG. 10. FIGS. 9through 12 show various embodiments of the sealing and connectorattachments of the present invention in capacitor 265.

FIG. 21 shows several top, perspective and cross-sectional viewsaccording to one embodiment of capacitor connector block 145 of thepresent invention. In preferred embodiments of connector block 145 ofthe present invention, connector block 145 is disposed atop or otherwiseconnected to case 90 and/or cover 110, and has wire harness 155 andpotting adhesive disposed therein.

A preferred material for forming connector block 145 is an injectionmolded polysulfone known as AMOCO UDEL supplied by Amoco PerformanceProducts of Atlanta, Ga. Connector block 140 may also be formed from anysuitable chemically resistant thermoplastic polymers such as aflouroplastic (e.g., ETFE, PTFE, ECTFE, or PCTFE, FEP, PFA, PVDF),polyester, polyamide, polyethylene, polypropylene, polyacetal,polyarylketone, polyether sulfone, polyphenyl sulfone, polysulfone,polyarylsulfone, polyetherimides, polyimide, poly(amide-imide), PVC,PVDC-PVC copolymer, CPVC, polyfuran, poly(phenylene sulfide), epoxyresin and fiber reinforced plastic.

In one embodiment of the present invention, connector block 145 isplaced on anode ferrule 95 and cathode ferrule 100 by guiding anodefeedthrough pin 130 through connector block anode feedthrough hole 300,and then guiding cathode feedthrough pin 135 through connector blockcathode feedthrough hole 305. Connector block 145 is next seated flushagainst the exterior surface of case 90. Anode feedthrough pin 130 isthen inserted into anode crimp tube 150b of wire harness 155. Cathodefeedthrough pin 135 is then inserted into cathode crimp tube 150a ofwire harness 155. Crimp tubes 150a and 150b are then crimped tofeedthrough pins 130 and 135.

In other embodiments of the present invention, electrical connections inconnector block 145 may be established using techniques such asultrasonic welding, resistance welding and laser welding. In suchjoining techniques, the joint geometry may also be a cross-wire weldbetween feedthrough wire 130 or 135 and harness wire 151 or 152. Thepresent invention includes within its scope an embodiment having case 90at cathode potential. In such an embodiment of the present invention, aseparate cathode terminal connection is most preferably provided topermit additional design flexibility.

The distal or basal portions of crimp tubes 150a and 150b are crimped oninsulated anode lead 151 and insulated cathode lead 152, respectively.Insulated leads 151 and 152 are likewise connected to terminal connector153. Terminal connector 153 may most preferably be connected toelectronics module 360. Standard methods of making aluminum electrolyticcapacitors do not lend themselves readily to very small crimpconnections, especially in miniaturized ICD designs. A method of thepresent invention permits small crimp connections an interconnectionmeans to be formed, and further permits highly efficient packaging inPCD 10.

In the preferred method described above, connector block 145 and epoxyadhesive provide strain relief to feedthrough pins 130 and 135 and tothe feedthrough wire crimp connections, and further provide an epoxyseal between pins 140 and 141, case 90 and ferrules 95 and 100. Thecrimp tubes may also serve as a connection point for device levelassembly. Alternatively, the crimp tubes may be integrated within wireharness 155 prior to capacitor assembly. The wire harness may then serveas a means of routing capacitor electrical connections as desired in,for example, device level assembly steps.

In the embodiment of the present invention shown in FIG. 11, terminalconnector 153 forms the female end of a slide contact. In anotherembodiment of the present invention, terminal connector 153 is connectedto other modules by resistance spot welding, ultrasonic wire bonding,soldering, crimping, or other attachment means.

Referring again to FIG. 21, insulated anode lead 151 is inserted intoanode block channel 310. Anode feedthrough pin 130 is centered inconnector block anode feedthrough hole 300 by anode pin block guide 320.Insulated cathode lead 152 is inserted into cathode block channel 315.Cathode feedthrough pin 135 is centered in connector block cathodefeedthrough hole 305 by cathode pin block guide 325. Centering of thepin through the ferrule assures that the pin does not contact theconducting wall of the ferrule, and also permits a more concentric epoxyseal to be formed around the pin. Centering of the pin may also beaccomplished through means disposed in or on the epoxy dispensing orcuring tools. Once the epoxy has hardened sufficiently, the centeringtool is removed.

When employed, a potting adhesive is mixed and dispensed throughconnector block feedthrough holes 300 and 305 and block channels 310 and315. Such an adhesive may also be dispensed through connector block hole330 between connector block 145 and case 90. Adhesive bonding betweenblock 145 and case 90 enhances structural stability of capacitor 265.The epoxy is then cured and capacitor 265 is filled with electrolyte.

The life of capacitor 265 may be appreciably shortened if solvent vaporor electrolyte fluid escapes from the interior of capacitor 265.Moreover, if capacitor 265 leaks electrolyte, the electrolyte may attackthe circuits to which capacitor 265 is connected, or may even provide aconductive pathway between portions of that circuit. The presentinvention provides a beneficial means for preventing the escape ofsolvent and solvent vapor from capacitor 265. More particularly,capacitor 265 most preferably includes hermetic laser welded seamsbetween joint case 90 and cover 110, and between ferrules 95, 100, and105 and case 90. Additionally, anode feedthrough portion 235 and cathodefeedthrough portion 240 most preferably have an adhesive seal disposedtherein for sealing the ferrule walls and the feedthrough wires.

The epoxy adhesive or potting material of the present invention is mostpreferably chemically resistant to the electrolyte employed in capacitor265 and adheres well to surrounding surfaces. Adhesion promotion (suchas by chemical deposition, etching, corona or plasma treatment of thepolymeric wire guide of a polymeric case) may be employed to maximizethe reliability of capacitor 265. In one preferred embodiment of thepresent invention, an aliphatic epoxy such as CIBA-Geigy Araldite 2014is employed. Other suitable potting adhesives include chemicallyresistant thermoplastic hot melt materials such as polyamides,polyesters, polyurethanes, epoxies, and polyethylene-vinyl acetates, UVcurable resins such as acrylates and methacrylates, and otherthermosetting resins such as aliphatic and aromatic epoxies, silicones,polyamides, polyesters and polyurethanes. Many suitable pottingadhesives may be thermally cured or cured with ultraviolet light. Afocused IR procedure may be employed in some instances to minimize curetime and localize heat.

Since hermeticity is desirable in feedthrough assemblies of the presentinvention, the method by which the feedthrough seals are made should bepredictable, uniform, reliable and produce high-quality hermetic seals.In a preferred method of the present invention, an epoxy adhesive isemployed which has few or no voids and cracks and completely orsubstantially completely adheres to the surrounding pin, ferrule walland wire guide components. Filling of the ferrule hole with sealingadhesive may be accomplished in several ways, depending largely on theviscosity of the potting agent selected. A balance in viscositycharacteristics of the sealing adhesive has been found to be desirable.More particularly, it is desired that the sealing adhesive be thinenough to fill without voids forming and to wet the surface, yet thickenough not to escape around or through the wire guide. The pottingadhesive may be B-staged and inserted as a plug; likewise a hot meltadhesive may be applied in similar fashion. Subsequent heating completescuring of the sealing adhesive. In a preferred method of the presentinvention, CIBA Geigy Araldite 2014 epoxy is mixed with a static mixtube and dispensed within 45 minutes. The assembly is cured in an ovenfor 30 minutes at 90 degrees Celsius.

In another embodiment of the present invention, connector block 145,ferrules 95 and 100, and wire guides 140 and 141 are formed from asingle molded component formed of a suitable chemically resistantthermoplastic or thermoset material that is sealed to case 90 using apotting adhesive. Channels or voids may be included in the basalportions of connector block 145 to permit potting adhesive to flowbetween those basal portions and case 90. Such a seal between the caseand connector block 145 may replace the aforementioned laser welded sealbetween the ferrule and the case. Such a sealing method eliminates therequirement for several components and removes several processing steps,leading perhaps to significant manufacturing cost reductions.

Referring again to FIG. 13, capacitor 265 is filled with electrolyte.The electrolyte may be any suitable liquid electrolyte for high voltageelectrolytic capacitors. In a preferred embodiment of the presentinvention, the electrolyte is an ethylene glycol based electrolytehaving an adipic acid solute. It is contemplated in the presentinvention that other electrolytes suitable for use in high voltagecapacitors may also be employed.

In accordance with a preferred method of the present invention,capacitor 265 is filled with a suitable liquid electrolyte via fill porttube 107 in multiple vacuum impregnation cycles. The capacitor and theelectrolyte are placed in a vacuum chamber with fill port tube 107connected to the electrolyte by a temporary tube. Multiple vacuumimpregnation cycles are then performed at pressures exceeding the vaporpressure of the electrolyte. In a less preferred method of the presentinvention, capacitor 265 is filled with electrolyte by immersingcapacitor 265 in the electrolyte or by vacuum-filling capacitor 265 witha metered filling machine. Note, however, that a single vacuumimpregnation cycle falls within the scope of at least one method of thepresent invention.

Fill port tube 107 of the present invention provides a means for fillingcapacitor 265. In preferred embodiments of the present invention, fillport tube 107 includes helium leak verification capabilities and easysealing characteristics. The hermeticity of capacitor 265 is preferablymeasured using a helium leak test. A helium leak testing apparatus formsa seal around the tube of fill port tube 107. The testing apparatus thenpulls a vacuum on the interior of sealed capacitor 265, and the gaspulled from the interior of capacitor 265 is directed past a tuned massspectrometer. Next, the exterior of capacitor 265 is exposed to heliumgas, and the leak rate for helium through the materials and jointswithin capacitor 265 is determined by the mass spectrometer. Thismeasure of leaktightness or hermeticity provides a means of assuring thequality of the joints being made.

In another embodiment of the present invention, "bombing" or filling ofthe interior of capacitor 265 with helium gas is accomplishedimmediately prior to sealing of fill port ferrule 105. The exterior ofsealed capacitor 265 is then monitored under vacuum conditions with atuned mass spectrometer to determine the rate of helium leakage past thematerials and joints of capacitor 265.

Once capacitor 265 is filled with electrolyte, it is preferred that anaging process be undertaken. Aging is generally accomplished by applyinga current through the capacitor terminals and gradually raising thevoltage across those terminals from zero to the peak aging voltage ofthe capacitor (usually between about 360 and about 390 Volts DC). Oncethe aging voltage is attained, capacitor 265 is held at that voltageuntil the leakage current stabilizes at an acceptably low value. It ispreferred that capacitor 265 be aged until a voltage of about 370 Voltsis attained during a current limiting process.

In one preferred method of the present invention, the aging process iscarried out with the voltage set at 370 Volts and the current limited toabout 1.5 mA (for capacitor 265 having a capacitance of 214microfarads). We have also found that it is beneficial to increase thetemperature of the aging system at higher voltages. In one preferredmethod of the present invention, the temperature is increased to about70 degrees Celsius when the voltage reaches 230 Volts. After aging to370 Volts, the capacitors are most preferably permitted to continueaging with the voltage held at 370 Volts until the leakage currentdecreases to a predetermined value, a predetermined time at 370 Voltshas elapsed, or until a predetermined rate of decrease in leakagecurrent has been obtained.

Following aging, post aging vacuum treatment or filling of the capacitorcontributes to significant improvements in capacitance and equivalentseries resistance (ESR). FIG. 22 shows a flow chart describing onemethod of vacuum treating the aged capacitor. The aged capacitor isplaced inside a vacuum chamber and held at 27 inches of mercury forthree minutes. The chamber is vented and then held at 27 inches ofmercury for three minutes for two additional cycles. The capacitor isthen provided for fill port sealing.

FIG. 23 shows a flow chart describing a preferred method for a vacuumrefilling operation after aging. Aged capacitor 265 is placed inside avacuum chamber, a temporary fill tube connected to fill port tube 107being immersed in electrolyte. The chamber is then held at 27 inches ofmercury for three minutes and vented. This step is repeated once withthe temporary tube in the electrolyte and a second time with thetemporary tube out of the electrolyte. The third cycle is intended todraw excess electrolyte from capacitor 265. Fillport ferrule tube 107 isnow ready for sealing.

FIG. 24 is a graph showing the increase in capacitance of fivecapacitors following the vacuum refilling operation of FIG. 23. Thenoted increase in capacitance is on the order of about 1 to about 2microfarads (˜0.3%). FIG. 25 is a graph showing the decrease in ESR ofthe same five capacitors after the vacuum refilling operation of FIG.23. The noted decrease in ESR is on the order of about 0.2 ohms (˜20%).The vacuum treatments are believed to remove entrapped gas that evolvesduring aging and refilling, and are also believed to replace electrolytelost during aging, thereby permitting the microstructural pores of theanode and separator layers to be substantially fully filled andsaturated with electrolyte. Excess electrolyte may also be removedthrough vacuum cycling with the fill tube pointing downwardly.

After vacuum refilling, distal end 106 of fill port tube 107 is mostpreferably crimped shut mechanically by pliers or other suitable meanssuch as compression rollers or welding. The crimped or closed joint soformed is next most preferably trimmed with side cutter metal shears orin a metal die, and sealed. It is an advantage of the present inventionthat the fill port thereof may be closed and sealed quickly at minimumcost without any requirement for additional high tolerance, expensivepiece parts or components for sealing fill tube 197.

Sealing of fill port tube 107 is most preferably accomplished usingjoining techniques such as ultrasonic welding, cold welding or laserwelding. See, for example, Tables 2 and 3. Sealing of fill port tube 107may also be accomplished by glueing, epoxying, or any other suitablemeans. For example, fill port tube 107 may be sealed by inserting acompression-fit spherical ball into a corresponding spherical recessdisposed inside fill port tube 107 or ferrule 105. The ball is mostpreferably formed from a metal, plastic or ceramic material that isstable in the capacitor electrolyte. Dimensional control of the fillport tube or ferrule inside diameter in respect of the diameter of theball is critical to controlling the quality of the seal being made.Ideally, the ball fits in the inside diameter in as tight aninterference fit as possible without damaging the fill port ferrule weldor deforming case 90 to any significant extent. The "ball" need notconform to a spherical geometry, and may be a fitting that iscylindrically, conically or otherwise-shaped.

Still another method for sealing fill port ferrule 105 is to integrate ahydrogen permeable membrane seal into or propinquant to fill portferrule 105 that does not permit electrolyte components to escapethrough fill port tube 107 but that does permit hydrogen gas evolvedthrough charge and discharge of capacitor 265 to escape from theinterior thereof. By sealing fill port tube 107 with a barrier havingsufficient chemical resistance, but that is selective to hydrogen gas(such as some silicones, polyphenylene oxides, cellulose acetates andtriacetates and polysulfones), no electrolyte is lost. Several pottingadhesives (such as epoxy or silicone) have the foregoing chemicalresistance and hydrogen permeability properties and thus are suitablefor use in the present invention. Those adhesives most preferably sealfeedthroughs while permitting hydrogen gas to escape from otherwisehermetically sealed capacitor 265.

In yet another embodiment of the present invention, the seal of fillport tube 107 is be a simple adhesive strip disposed over distal end 106of fill port tube 107, similar to the types of seals employed incommercial ethylene glycol coolant canisters.

It is preferred that fill port ferrule 105 and fill port tube 107 form asingle integrated piece of metal, although components 105 and 107 mayform separate non-integral components and may further be formed ofmaterials other than metal, such as ceramic or plastic. Fill portferrule 105 fits within and is sealingly engaged to an opening disposedin the sidewall of case 90 or in cover 110. Additionally, height 109 offill port tube 107 shown in FIG. 28(c) is most preferably about 0.200inches with respect to the embodiment of capacitor 265 shown in thedrawings hereof, although other heights 109 are contemplated in thepresent invention such as 0.065 inches, 0.300 inches, and so on.

It is preferred that height 109 be sufficiently great to accommodate afitting of a helium leaktightness testing apparatus, the fitting beingfitted in sealing engagement over the fill tube. It is preferred that anO-ring be disposed between the fitting and the fill tube as a vacuum ofabout 50 Tor is pulled on the interior of capacitor 265. Helium gas isthen emitted about and around capacitor 265, cover 110, case 90, joint93 between cover 110 and case 90, connector block 145, ferrule 105, tube107 and other components while the helium leaktightness testingapparatus tests gas and molecules evacuated from the interior ofcapacitor 265 for the presence of helium gas which has leaked from theexterior of capacitor 265 into the interior thereof.

A tuned mass spectrometer is most preferably included in the heliumleaktightness testing apparatus. The spectrometer is sensitive to thepresence of helium atoms or molecules. An example of such an apparatusis a LEYBOLD INFICON Model No. UL-200 Helium Leaktester manufactured inEast Syracuse, N.Y. An O-ring having a leaktightness rating of about1×10⁻⁹ cm³ /sec. is most preferably employed in conjunction with thefill tube and the fitting of the leaktightness testing apparatus. Atypical fail point specification for the leaktightness testing apparatuswhen employed with the capacitor of the present invention is about1×10⁻⁹ cm³ /sec.

FIG. 27(a) shows a top view of capacitor 265 with a portion of cover 90removed and a portion of electrode assembly 225 exposed therewithin.Fill port ferrule tube 107 projects outwardly from an end of case 90from fill port ferrule 105. FIG. 27(b) shows an end view of capacitor265 of FIG. 27(a), and a corresponding end view of fill port tube 107and fill port ferrule 105. FIGS. 28(a) through 28(c) show various viewsof one embodiment of liquid electrolyte fill port tube 107 and fill portferrule 105 of the present invention.

In another embodiment of fill port tube 107 of the present invention,case 90 is formed of a suitable metal, and a fill port tube 107 isextruded from, punched in or otherwise integrally formed in a sidewallor other portion of case 90. Such a design eliminates the need for fillport ferrule 105 disposed in a wall or surface of case 90. For example,a tapered punch may be employed to initially punch a small diameter holein a sidewall of case 90, followed by causing the punch to travelthrough the hole, causing metal from sidewall 90 to be extrudedoutwardly from the sidewall, and forming an outwardly projectingcylindrically or otherwise shaped fill port tube 107.

Once sealed, the capacitor is electrically tested. Applications inimplantable defibrillators may require two capacitors to be connected inseries. In this case an insulator is provided by a two sided adhesivebeing disposed between the capacitors. Two capacitors are joined alongopposing faces with the insulator/adhesive strip disposed therebetween.The pair of capacitors is then provided for assembly in PCD 10. SeeFIGS. 3(a) through 3(h).

The scope of the present invention is not limited to defibrillation orcardioversion applications, or to applications where a human heart isdefibrillated, but includes similar applications in other mammalians andmammalian organs. Those of ordinary skill will now appreciate that themethod and device of the present invention are not limited to aluminumelectrolytic capacitors for implantable medical devices, but extend tonon-aluminum or partially-aluminum electrolytic capacitors forimplantable medical devices, as well as to methods and correspondingcapacitors and power sources for non-implantable medical devices and forelectronic devices generally.

Additionally, although only a few exemplary embodiments of the presentinvention have been described in detail above, those skilled in the artwill appreciate readily that many modifications are possible in theexemplary embodiments without materially departing from the novelteachings and advantages of the invention. Accordingly, all suchmodifications are intended to be included within the scope of thepresent invention as defined in the following claims.

The preceding specific embodiments are illustrative of the practice ofthe invention. It is to be understood, therefore, that other expedientsknown to those skilled in the art or disclosed herein, may be employedwithout departing from the invention or the scope of the appendedclaims.

In the claims, means-plus-function clauses are intended to cover thestructures described herein as performing the recited function and notonly structural equivalents but also equivalent structures. Thus,although a nail and a screw may not be structural equivalents in that anail employs a cylindrical surface to secure wooden parts together,whereas a screw employs a helical surface, in the environment offastening wooden parts a nail and a screw are equivalent structures.

All patents and printed publications disclosed hereinabove are herebyincorporated by reference herein into the specification hereof, each inits respective entirety.

We claim:
 1. An hermetically sealed implantable medical device,comprising:(a) an hermetically sealed housing; (b) an energy sourcedisposed within the housing; (c) a substantially flat electrolyticcapacitor connected to the energy source and disposed within thehousing, the capacitor comprising:(i) at least one flat cathode layerformed of cathode foil; (ii) a plurality of cold-welded flat anodelayers formed of anode foil, the plurality of cold-welded anode layersforming an anode sub-assembly having a thickness T and top and bottomsurfaces, the top and bottom surfaces of the anode sub-assembly havingcorresponding at least one vertically-aligned cold-welded region formedthereon, the at least one cold-welded region of the anode sub-assemblyhaving a thickness T+ΔT, the ratio ΔT/T of the anode sub-assembly beingless than or equal to 0.50; (iii) at least a first separator layerformed of separator material and defined by a third perimeter; (iv) acapacitor case having sidewalls extending upwardly from a substantiallyflat planar base to form an open end; (v) a cover for sealing the openend of the capacitor case, the cover being disposed over andhermetically sealing the open end of the case;wherein the at least onecathode layer, the anode sub-assembly and the first separator layer arevertically stacked in the case such that the first separator layer isdisposed between the at least one cathode layer and the anodesub-assembly.
 2. The implantable medical device of claim 1, wherein theat least one cathode layer has no holes for registration disposedtherethrough.
 3. The implantable medical device of claim 1, wherein theplurality of anode layers have no holes for registration disposedtherethrough.
 4. The implantable medical device of claim 1, wherein thecase is formed of aluminum or aluminum alloy.
 5. The implantable medicaldevice of claim 1, wherein the cover is formed of aluminum or aluminumalloy.
 6. The implantable medical device of claim 1, wherein the atleast one cathode layer is formed of aluminum cathode foil.
 7. Theimplantable medical device of claim 1, wherein the anode layers areformed of through-etched aluminum anode foil.
 8. The implantable medicaldevice of claim 1, wherein each anode layer has a specific capacitanceselected from the group consisting of at least about 0.3microfarads/cm², at least about 0.5 microfarads/cm², and at least about0.8 microfarads/cm².
 9. The implantable medical device of claim 1,wherein each anode layer has a thickness selected from the groupconsisting of from about 20 micrometers to about 300 micrometers, fromabout 40 micrometers to about 200 micrometers, from about 60 micrometersto about 150 micrometers, and from about 70 micrometers to about 140micrometers.
 10. The implantable medical device of claim 1, wherein theat least one cathode layer is formed from a highly etched cathode foil.11. The implantable medical device of claim 1, wherein the at least onecathode layer is formed from a cathode foil having a specificcapacitance selected from the group consisting of at least about 100microfarads/cm², at least about 200 microfarads/cm², at least about 250microfarads/cm², and at least about 300 microfarads/cm².
 12. Theimplantable medical device of claim 1, wherein the at least one cathodelayer is formed from foil having a thickness selected from the groupconsisting of from about 10 micrometers to about 200 micrometers, fromabout 15 micrometers to about 150 micrometers, from about 20 micrometersto about 100 micrometers, from about 25 micrometers to about 75micrometers, and about 30 micrometers.
 13. The implantable medicaldevice of claim 1, wherein the anode sub-assembly comprises a pluralityof non-notched anode layers and at least one notched anode layer. 14.The implantable medical device of claim 1, wherein the first separatorlayer is pressure bonded to the anode sub-assembly.
 15. The implantablemedical device of claim 1, wherein the top and bottom surfaces of theanode sub-assembly are covered by the first separator layer and a secondseparator layer.
 16. The implantable medical device of claim 1, whereinthe top and bottom surfaces of the at least one cathode layer arecovered by the first separator layer and a second separator layer. 17.The implantable medical device of claim 1, wherein the implantablemedical device is selected from the group consisting of a PCD, an AID,an ICD, a defibrillator, an implantable pulse generator and a pacemaker.18. The implantable medical device claim 1, wherein the energy source isselected from the group consisting of a battery, an electrochemicalcell, a primary electrochemical cell, a secondary or rechargeableelectrochemical cell, an electrochemical cell comprising alithium-containing anode, an electrochemical cell comprising a silvervanadium oxide-containing cathode, an electrochemical cell comprising a(CF_(n))_(x) -containing cathode, an electrochemical cell comprising acathode containing a mixture of silver vanadium oxide and (CF_(n))_(x),a spirally wound electrochemical cell, an electrochemical cell having aplurality of plate-shaped electrodes, and an electrochemical cell havingat least one serpentine electrode disposed therewithin.
 19. Theimplantable medical device of claim 1, wherein the plurality of anodelayers are connected electrically to the case.
 20. The implantablemedical device of claim 1, wherein the at least one cathode layer iselectrically connected to the case.
 21. The implantable medical deviceof claim 1, wherein the case is connected electrically to neither the atleast one cathode layer nor to the plurality of anode layers.
 22. Theimplantable medical device of claim 1, wherein at least one anode layerthereof has a tab formed or attached to a perimeter thereof.
 23. Theimplantable medical device of claim 22, wherein the tab is formed ofaluminum.
 24. The implantable medical device of claim 23, wherein thetab is formed of aluminum having a purity of about 99.99% aluminum. 25.The implantable medical device of claim 1, wherein the ratio ΔT/T of theanode sub-assembly is less than or equal to 0.50.
 26. The implantablemedical device of claim 1, wherein the ratio ΔT/T of the anodesub-assembly is less than or equal to 0.45.
 27. The implantable medicaldevice of claim 1, wherein the ratio ΔT/T of the anode sub-assembly isless than or equal to 0.40.
 28. The implantable medical device of claim1, wherein the ratio ΔT/T of the anode sub-assembly is less than orequal to 0.35.
 29. The implantable medical device of claim 1, whereinthe ratio ΔT/T of the anode sub-assembly is less than or equal to 0.30.30. The implantable medical device of claim 1, wherein the ratio ΔT/T ofthe anode sub-assembly is less than or equal to 0.25.
 31. Theimplantable medical device of claim 1, wherein the ratio ΔT/T of theanode sub-assembly is less than or equal to 0.20.
 32. The implantablemedical device of claim 1, wherein the ratio ΔT/T of the anodesub-assembly is less than or equal to 0.15.
 33. The implantable medicaldevice of claim 1, wherein the ratio ΔT/T of the anode sub-assembly isless than or equal to 0.10.
 34. The implantable medical device of claim1, wherein the ratio ΔT/T of the anode sub-assembly is less than orequal to 0.05.
 35. The implantable medical device of claim 1, whereinthe anode sub-assembly has a plurality of tabbed anode layers containedtherein, each such layer having an anode tab attached to a perimeterthereof.
 36. The implantable medical device of claim 35, wherein therespective tabs of the tabbed anode layers are offset horizontally inrespect of one another to reduce the thickness of the anodesub-assembly.
 37. A substantially flat electrolytic capacitor,comprising:(a) at least one flat cathode layer formed of cathode foil;(b) a plurality of cold-welded flat anode layers formed of anode foil,the plurality of cold-welded anode layers forming an anode sub-assemblyhaving a thickness T and top and bottom surfaces, the top and bottomsurfaces of the anode sub-assembly having corresponding at least onevertically-aligned cold-welded region formed thereon, the at least onecold-welded region of the anode sub-assembly having a thickness T+ΔT,the ratio ΔT/T of the anode sub-assembly being less than or equal to0.50; (c) at least a first separator layer formed of separator materialand defined by a third perimeter; (d) a capacitor case having sidewallsextending upwardly from a substantially flat planar base to form an openend; (e) a cover for sealing the open end of the capacitor case, thecover being disposed over and hermetically sealing the open end of thecase;wherein the at least one cathode layer, the anode sub-assembly andthe first separator layer are vertically stacked in the case such thatthe first separator layer is disposed between the at least one cathodelayer and the anode sub-assembly.
 38. The implantable medical device ofclaim 37, wherein the at least one cathode layer has no holes forregistration disposed therethrough.
 39. The implantable medical deviceof claim 37, wherein the plurality of anode layers have no holes forregistration disposed therethrough.
 40. The implantable medical deviceof claim 37, wherein the case is formed of aluminum or aluminum alloy.41. The implantable medical device of claim 37, wherein the cover isformed of aluminum or aluminum alloy.
 42. The implantable medical deviceof claim 37, wherein the at least one cathode layer is formed ofaluminum cathode foil.
 43. The implantable medical device of claim 37,wherein the anode layers are formed of through-etched aluminum anodefoil.
 44. The implantable medical device of claim 37, wherein each anodelayer has a specific capacitance selected from the group consisting ofat least about 0.3 microfarads/cm², at least about 0.5 microfarads/cm²,and at least about 0.8 microfarads/cm².
 45. The implantable medicaldevice of claim 37, wherein each anode layer has a thickness selectedfrom the group consisting of from about 20 micrometers to about 300micrometers, from about 40 micrometers to about 200 micrometers, fromabout 60 micrometers to about 150 micrometers, and from about 70micrometers to about 140 micrometers.
 46. The implantable medical deviceof claim 37, wherein the at least one cathode layer is formed from ahighly etched cathode foil.
 47. The implantable medical device of claim37, wherein the at least one cathode layer is formed from a cathode foilhaving a specific capacitance selected from the group consisting of atleast about 100 microfaradscm², at least about 200 microfaradscm², atleast about 250 microfaradscm², and at least about 300 microfarads/cm².48. The implantable medical device of claim 37, wherein the at least onecathode layer is formed from foil having a thickness selected from thegroup consisting of from about 10 micrometers to about 200 micrometers,from about 15 micrometers to about 150 micrometers, from about 20micrometers to about 100 micrometers, from about 25 micrometers to about75 micrometers, and about 30 micrometers.
 49. The implantable medicaldevice of claim 37, wherein the anode sub-assembly comprises a pluralityof non-notched anode layers and at least one notched anode layer. 50.The implantable medical device of claim 37, wherein the first separatorlayer is pressure bonded to the anode sub-assembly.
 51. The implantablemedical device of claim 37, wherein the top and bottom surfaces of theanode sub-assembly are covered by the first separator layer and a secondseparator layer.
 52. The implantable medical device of claim 37, whereinthe top and bottom surfaces of the at least one cathode layer arecovered by the first separator layer and a second separator layer. 53.The implantable medical device of claim 37, wherein the implantablemedical device is selected from the group consisting of a PCD, an AID,an ICD, a defibrillator, an implantable pulse generator and a pacemaker.54. The implantable medical device claim 37, wherein the energy sourceis selected from the group consisting of a battery, an electrochemicalcell, a primary electrochemical cell, a secondary or rechargeableelectrochemical cell, an electrochemical cell comprising alithium-containing anode, an electrochemical cell comprising a silvervanadium oxide-containing cathode, an electrochemical cell comprising a(CF_(n))_(x) -containing cathode, an electrochemical cell comprising acathode containing a mixture of silver vanadium oxide and (CF_(n))_(x),a spirally wound electrochemical cell, an electrochemical cell having aplurality of plate-shaped electrodes, and an electrochemical cell havingat least one serpentine electrode disposed therewithin.
 55. Theimplantable medical device of claim 37, wherein the plurality of anodelayers are connected electrically to the case.
 56. The implantablemedical device of claim 37, wherein the at least one cathode layer iselectrically connected to the case.
 57. The implantable medical deviceof claim 37, wherein the case is connected electrically to neither theat least one cathode layer nor to the plurality of anode layers.
 58. Theimplantable medical device of claim 37, wherein at least one anode layerthereof has a tab formed or attached to a perimeter thereof.
 59. Theimplantable medical device of claim 58, wherein the tab is formed ofaluminum.
 60. The implantable medical device of claim 59 wherein the tabis formed of aluminum having a purity of about 99.99% aluminum.
 61. Theimplantable medical device of claim 37, wherein the ratio ΔT/T of theanode sub-assembly is less than or equal to 0.50.
 62. The implantablemedical device of claim 37, wherein the ratio ΔT/T of the anodesub-assembly is less than or equal to 0.45.
 63. The implantable medicaldevice of claim 37, wherein the ratio ΔT/T of the anode sub-assembly isless than or equal to 0.40.
 64. The implantable medical device of claim37, wherein the ratio ΔT/T of the anode sub-assembly is less than orequal to 0.35.
 65. The implantable medical device of claim 37, whereinthe ratio ΔT/T of the anode sub-assembly is less than or equal to 0.30.66. The implantable medical device of claim 37, wherein the ratio ΔT/Tof the anode sub-assembly is less than or equal to 0.25.
 67. Theimplantable medical device of claim 37, wherein the ratio ΔT/T of theanode sub-assembly is less than or equal to 0.20.
 68. The implantablemedical device of claim 37, wherein the ratio ΔT/T of the anodesub-assembly is less than or equal to 0.15.
 69. The implantable medicaldevice of claim 37, wherein the ratio ΔT/T of the anode sub-assembly isless than or equal to 0.10.
 70. The implantable medical device of claim37, wherein the ratio ΔT/T of the anode sub-assembly is less than orequal to 0.05.
 71. The implantable medical device of claim 37, whereinthe anode sub-assembly has a plurality of tabbed anode layers containedtherein, each such layer having an anode tab attached to a perimeterthereof.
 72. The implantable medical device of claim 71, wherein therespective tabs of the tabbed anode layers are offset horizontally inrespect of one another to reduce the thickness of the anodesub-assembly.
 73. A method of making an hermetically sealed implantablemedical device, comprising the steps of:(a) providing a housing for theimplantable medical device; (b) providing an energy source for theimplantable medical device and disposing the energy source within thehousing; (c) forming a substantially flat electrolytic capacitor,comprising the steps of:(i) providing at least one cathode layer formedof cathode foil; (ii) providing a plurality of anode layers formed ofanode foil; (iii) vertically stacking the plurality of anode layers toform an anode sub-assembly having top and bottom surfaces and athickness T; (iv) cold welding the anode sub-assembly such that the topand bottom surfaces of the anode sub-assembly have at least onevertically-aligned cold-welded region formed thereon, the at least onecold-welded region of the anode sub-assembly has a thickness T+ΔT, andthe ratio ΔT/T of the anode sub-assembly is less than or equal to 0.50;(v) providing at least a first separator layer formed of separatormaterial; (vi) vertically stacking the at least one cathode layer, thecold-welded anode sub-assembly and the first separator layer such thatthe first separator layer is disposed between the at least one cathodelayer and the anode sub-assembly to form a capacitor electrode assembly;(vii) placing the electrode assembly in a capacitor case having an openend; (viii) placing a cover over the open end of the case; (ix) joiningthe cover to the case; (d) disposing the capacitor in the housing; (e)connecting the capacitor to the power source, and (f) hermeticallysealing the housing.
 74. The method of claim 73, wherein the cathodelayer providing step is preceded by a step of forming the cathode layerfrom an aluminum cathode foil.
 75. The method of claim 73, wherein theanode layer providing step is preceded by a step of forming theplurality of anode layers from through-etched aluminum anode foil. 76.The method of claim 75, wherein the anode layer forming step furthercomprises the step of providing aluminum anode foil having a specificcapacitance selected from the group consisting of at least about 0.3microfarads/cm², at least about 0.5 microfarads/cm², and at least about0.8 microfarads/cm² for each anode layer contained therein.
 77. Themethod of claim 75, wherein the anode layer forming step furthercomprises the step of providing, for each anode layer contained in thecapacitor, aluminum anode foil having a thickness selected from thegroup consisting of from about 20 micrometers to about 300 micrometers,from about 40 micrometers to about 200 micrometers, from about 60micrometers to about 150 micrometers, and about 70 micrometers to about140 micrometers.
 78. The method of claim 75, wherein the anode layerforming step further comprises the step of attaching the second tab tothe second perimeter at the second location in the first anode layer.79. The method of claim 75, wherein the cathode layer providing step ispreceded by a step of forming the at least one cathode layer from ahighly etched cathode foil.
 80. The method of claim 79, wherein thecathode layer forming step further comprises the step of providingcathode foil having a specific capacitance selected from the groupconsisting of at least about 100 microfarads/cm², at least about 200microfarads/cm², at least about 250 microfarads/cm², and at least about300 microfarads/cm².
 81. The method of claim 79, wherein the cathodelayer forming step further comprises the step of providing cathode foilhaving a thickness selected from the group consisting of from about 10micrometers to about 200 micrometers, from about 15 micrometers to about150 micrometers, from about 20 micrometers to about 100 micrometers,from about 25 micrometers to about 75 micrometers, and about 30micrometers.
 82. The method of claim 79, wherein the cathode layerforming step further comprises the step of providing cathode foil havinga purity of at least about 99%.
 83. The method of claim 73, wherein theanode layer forming step further comprises the step of providingaluminum anode foil having a purity of at least about 99.9%.
 84. Themethod of claim 73, wherein the anode layer providing step is precededby a step of selecting a plurality of non-notched anode layers and atleast one notched anode layer for inclusion in the anode sub-assembly.85. The method of claim 73, wherein the first separator layer providingstep is preceded by a step of forming the first separator layers fromKraft paper.
 86. The method of claim 73, wherein the anode layerproviding step and the separator layer providing step are preceded by astep of pressure bonding the first separator layer to the anodesub-assembly.
 87. The method of claim 73, wherein the anode layerproviding step and the separator layer providing step are preceded by astep of covering the top and bottom surfaces of the anode sub-assemblywith the first separator layer and a second separator layer.
 88. Themethod of claim 73, further comprising the step of securing a free edgeof the first separator layer with tape, adhesive or stitching or byultrasonic paper welding.
 89. The method of claim 73, wherein thecathode layer providing step and the separator layer providing step arepreceded by a step of covering the top and bottom surfaces of the atleast one cathode layer with the first separator layer and a secondseparator layer.
 90. The method of claim 89, further comprising the stepof securing a free edge of the first separator layer with tape, adhesiveor stitching or by ultrasonic paper welding.
 91. The method of claim 89,further comprising the step of securing a free edge of the firstseparator layer with tape, adhesive or stitching or by ultrasonic paperwelding.
 92. The method of claim 73, wherein the step of verticallystacking the at least one cathode layer, the anode sub-assembly and theseparator layer further comprises providing a stacking fixture forregistration of the layers therein as the layers are stacked in thefixture.
 93. The method of claim 73, further comprising the step ofwrapping the stacked electrode assembly with an outer wrap.
 94. Themethod of claim 93, further comprising the step of securing the outerwrap to the stacked electrode assembly with tape.
 95. The method ofclaim 93, further comprising the step of securing the outer wrap to thestacked electrode assembly with tape.
 96. The method of claim 73,wherein the anode sub-assembly cold welding step is carried out suchthat the at least one cold-welded region of the anode sub-assembly has athickness T+ΔT and the ratio ΔT/T is less than or equal to 0.45.
 97. Themethod of claim 73, wherein the anode sub-assembly cold welding step iscarried out such that the at least one cold-welded region of the anodesub-assembly has a thickness T+ΔT and the ratio ΔT/T is less than orequal to 0.40.
 98. The method of claim 73, wherein the anodesub-assembly cold welding step is carried out such that the at least onecold-welded region of the anode sub-assembly has a thickness T+ΔT andthe ratio ΔT/T is less than or equal to 0.35.
 99. The method of claim73, wherein the anode sub-assembly cold welding step is carried out suchthat the at least one cold-welded region of the anode sub-assembly has athickness T+ΔT and the ratio ΔT/T is less than or equal to 0.30. 100.The method of claim 73, wherein the anode sub-assembly cold welding stepis carried out such that the at least one cold-welded region of theanode sub-assembly has a thickness T+ΔT and the ratio ΔT/T is less thanor equal to 0.25.
 101. The method of claim 73, wherein the anodesub-assembly cold welding step is carried out such that the at least onecold-welded region of the anode sub-assembly has a thickness T+ΔT andthe ratio ΔT/T is less than or equal to 0.20.
 102. The method of claim73, wherein the anode sub-assembly cold welding step is carried out suchthat the at least one cold-welded region of the anode sub-assembly has athickness T+ΔT and the ratio ΔT/T is less than or equal to 0.15. 103.The method of claim 73, wherein the anode sub-assembly cold welding stepis carried out such that the at least one cold-welded region of theanode sub-assembly has a thickness T+ΔT and the ratio ΔT/T is less thanor equal to 0.10.
 104. The method of claim 73, wherein the anodesub-assembly cold welding step is carried out such that the at least onecold-welded region of the anode sub-assembly has a thickness T+ΔT andthe ratio ΔT/T is less than or equal to 0.05.
 105. A method of making asubstantially flat electrolytic capacitor, comprising the steps of:(a)providing at least one cathode layer formed of cathode foil; (b)providing a plurality of anode layers formed of anode foil; (c)vertically stacking the plurality of anode layers to form an anodesub-assembly having top and bottom surfaces and a thickness T; (d) coldwelding the anode sub-assembly such that the top and bottom surfaces ofthe anode sub-assembly have at least one vertically-aligned cold-weldedregion formed thereon, the at least one cold-welded region of the anodesub-assembly has a thickness T+ΔT, and the ratio ΔT/T of the anodesub-assembly is less than or equal to 0.50; (e) providing at least afirst separator layer formed of separator material; (f) verticallystacking the at least one cathode layer, the cold-welded anodesub-assembly and the first separator layer such that the first separatorlayer is disposed between the at least one cathode layer and the anodesub-assembly to form a capacitor electrode assembly; (g) placing theelectrode assembly in a capacitor case having an open end; (h) placing acover over the open end of the case, and (i) joining the cover to thecase.
 106. The method of claim 105, wherein the cathode layer providingstep is preceded by a step of forming the cathode layer from an aluminumcathode foil.
 107. The method of claim 105, wherein the anode layerproviding step is preceded by a step of forming the plurality of anodelayers from through-etched aluminum anode foil.
 108. The method of claim107, wherein the anode layer forming step further comprises the step ofproviding aluminum anode foil having a purity of at least about 99.9%.109. The method of claim 107, wherein the anode layer forming stepfurther comprises the step of providing aluminum anode foil having aspecific capacitance selected from the group consisting of at leastabout 0.3 microfarads/cm², at least about 0.5 microfarads/cm², and atleast about 0.8 microfarads/cm² for each anode layer contained therein.110. The method of claim 107, wherein the anode layer forming stepfurther comprises the step of providing, for each anode layer containedin the capacitor, aluminum anode foil having a thickness selected fromthe group consisting of from about 20 micrometers to about 300micrometers, from about 40 micrometers to about 200 micrometers, fromabout 60 micrometers to about 150 micrometers, and about 70 micrometersto about 140 micrometers.
 111. The method of claim 107, wherein theanode layer forming step further comprises the step of attaching thesecond tab to the second perimeter at the second location in the firstanode layer.
 112. The method of claim 107, wherein the cathode layerproviding step is preceded by a step of forming the at least one cathodelayer from a highly etched cathode foil.
 113. The method of claim 112,wherein the cathode layer forming step further comprises the step ofproviding cathode foil having a specific capacitance selected from thegroup consisting of at least about 100 microfarads/cm², at least about200 microfarads/cm², at least about 250 microfarads/cm², and at leastabout 300 microfarads/cm².
 114. The method of claim 112, wherein thecathode layer forming step further comprises the step of providingcathode foil having a thickness selected from the group consisting offrom about 10 micrometers to about 200 micrometers, from about 15micrometers to about 150 micrometers, from about 20 micrometers to about100 micrometers, from about 25 micrometers to about 75 micrometers, andabout 30 micrometers.
 115. The method of claim 112, wherein the cathodelayer forming step further comprises the step of providing cathode foilhaving a purity of at least about 99%.
 116. The method of claim 105,wherein the anode layer providing step is preceded by a step ofselecting a plurality of non-notched anode layers and at least onenotched anode layer for inclusion in the anode sub-assembly.
 117. Themethod of claim 105, wherein the first separator layer providing step ispreceded by a step of forming the first separator layers from Kraftpaper.
 118. The method of claim 105, wherein the anode layer providingstep and the separator layer providing step are preceded by a step ofpressure bonding the first separator layer to the anode sub-assembly.119. The method of claim 105, wherein the anode layer providing step andthe separator layer providing step are preceded by a step of coveringthe top and bottom surfaces of the anode sub-assembly with the firstseparator layer and a second separator layer.
 120. The method of claim105, further comprising the step of securing a free edge of the firstseparator layer with tape, adhesive or stitching or by ultrasonic paperwelding.
 121. The method of claim 105, wherein the cathode layerproviding step and the separator layer providing step are preceded by astep of covering the top and bottom surfaces of the at least one cathodelayer with the first separator layer and a second separator layer. 122.The method of claim 105, wherein the step of vertically stacking the atleast one cathode layer, the anode sub-assembly and the separator layerfurther comprises providing a stacking fixture for registration of thelayers therein as the layers are stacked in the fixture.
 123. The methodof claim 105, further comprising the step of wrapping the stackedelectrode assembly with an outer wrap.
 124. The method of claim 105,wherein the anode sub-assembly cold welding step is carried out suchthat the at least one cold-welded region of the anode sub-assembly has athickness T+ΔT and the ratio ΔT/T is less than or equal to 0.45. 125.The method of claim 105, wherein the anode sub-assembly cold weldingstep is carried out such that the at least one cold-welded region of theanode sub-assembly has a thickness T+ΔT and the ratio ΔT/T is less thanor equal to 0.40.
 126. The method of claim 105, wherein the anodesub-assembly cold welding step is carried out such that the at least onecold-welded region of the anode sub-assembly has a thickness T+ΔT andthe ratio ΔT/T is less than or equal to 0.35.
 127. The method of claim105, wherein the anode sub-assembly cold welding step is carried outsuch that the at least one cold-welded region of the anode sub-assemblyhas a thickness T+ΔT and the ratio ΔT/T is less than or equal to 0.30.128. The method of claim 105, wherein the anode sub-assembly coldwelding step is carried out such that the at least one cold-weldedregion of the anode sub-assembly has a thickness T+ΔT and the ratio ΔT/Tis less than or equal to 0.25.
 129. The method of claim 105, wherein theanode sub-assembly cold welding step is carried out such that the atleast one cold-welded region of the anode sub-assembly has a thicknessT+ΔT and the ratio ΔT/T is less than or equal to 0.20.
 130. The methodof claim 105, wherein the anode sub-assembly cold welding step iscarried out such that the at least one cold-welded region of the anodesub-assembly has a thickness T+ΔT and the ratio ΔT/T is less than orequal to 0.15.
 131. The method of claim 105, wherein the anodesub-assembly cold welding step is carried out such that the at least onecold-welded region of the anode sub-assembly has a thickness T+ΔT andthe ratio ΔT/T is less than or equal to 0.10.
 132. The method of claim105, wherein the anode sub-assembly cold welding step is carried outsuch that the at least one cold-welded region of the anode sub-assemblyhas a thickness T+ΔT and the ratio ΔT/T is less than or equal to 0.05.